Look, tempo is a musical concept, and finding the beat is a human cognitive exercise. A computer program cannot "feel the beat," but it can search for changes in volume, and look for repetitive patterns over time to extact a best guess about what the tempo might be. That works best if the changes are sudden and brief (transients) and very regular, which is why programs that do this work best with things like drum tracks, and not very well with extended pads or string sections. Yes, you should count the beat with your brain when the computer is obviously wrong.
If all of the beats of the all of the tracks of your own recorded music line up with each other, they are in synch relative to each other. If there is some variation of the recorded beats from the metronome beats they are "drifting" or "wandering" relative to the metronome. If the beats can all be synchronized to the metronome they are "on the beat," and "in time." If the beats do not all line up with the metronome, but they can be sychronized to the metronome by changing the tempo of the metronome, they are on the beat, but fast or slow relative to the tempo/time--"off time." In that case they will be "drifting" relative to the metronome and each sucessive beat will gradually be getting further from the metronome beat it should land on. If it is impossible to sychonize the beat to the metronome at any speed they are "wandering" relative to the metronome and they are off beat. It is actually not unusual for human performances to not line up with the metronome. Gradual changes in tempo, or holding or rushing one or a few beats at a time are part of the musical expression of a piece, or just human error. But if they do stay on beat, it makes your problem easier.
If both of a set of tracks that do not line up with each other still line up with the metronome/click track but only when the metronome is at a different "tempo" for some of the tracks (they are invariably on the beat), then the non-aligned tracks have the property that there is a fixed ratio between the beats/music delivered per second in the one to the other. In that case a "stretch" algorithm that lengthens the one at the faster tempo (or shortens the slower one) and distributes the additional time equally along the track can bring them into exact alignment a whole track at a time.
If there is beat to beat variation within the track (off beat) then stretching the whole track will not bring the beats into synch with either the metronome or another track that is on the beat or is off beat on different beats. You still need to perform a stretch, but you have to do it on a smaller chunk of the track at a time, often a single beat or less if you are really anal about lining things up. There are ways to automate parts of that task, and one of the least labor intensive for the quality of the result is the Audiosnap plugin. It is still nowhere near as simple as changing the "tempo," and for a skilled performer nowhere near as fast as recording another take. Ask someone else how to do that, I work almost exclusively in MIDI.
Now as to the "tempo" in Sonar, and in MIDI in general. MIDI tempo is not musical tempo, it is simply an alias for real time that is useful for relating notated musical onset and duration with actual control of a musical performance. A human performance on a MIDI controller is actually a recording of the real time (not the musical time) at which an instrument should sound quantized to ticks per quarter note at the rate of the quarter notes per minute set as the MIDI tempo. Unless the performer is perfectly in time with a synchronized metronome or some type of quantization is applied it will not sit on a particular quarter note division boundary any more than the sound of a wood and wire piano hammer will sit perfectly on the beat. But because MIDI tempo directly relates to the time, and there is no complicated DSP gymnastics needed to move a note-on it is easier to design a computer algorithm to fix problems with time in MIDI. If you want to keep the same expressive options of moving off the beat or changing tempo beat to beat however, instead of just jamming everything onto the nearest note division, it is still not as simple as just changing the tempo to line up two tracks that are not perfectly on the beat with each other.
At any rate, since Sonar's tempo setting just controls the MIDI clock (actually the number of quarter notes/ticks per minute), changing the Sonar tempo will have no effect on recorded audio, which is controlled by a clock that reads in digital samples per second and does not relate either to the musical beat or tempo. You can import or export at different tempo or change the tempo in Sonar to anything you want and the asynchronous audio tracks will not change their recorded tempo at all unless they are set up with another technique that automatically stretches to tempo like groove clips. And then they will only align perfectly if the two are perfectly on beat in their original tempo.
NB: This is pretty much what I said in my previous post, but hopefully the expanded version will make more sense to you.