I sometimes collaborate on music. Someone provides me with a rough audio track, and want to build on it.
I want to match the Sonar project tempo to the audio track.  Usually the track has a constant tempo, so I don't need to have a widely varying tempo map. Just quickly find the tempo of the track and get it onto the project grid.
 
Sonar has "fit to time" and "fit improvisation" but they don't do the right thing. Every time a new version of Sonar comes out, I  try to get "fit improvisation" to do something that makes sense, and eventually give up.
I usually end up using "tap tempo" on my Kronos, or counting out the number of beats and measures and calculating the tempo based on the total time.
 
Is there any way Sonar can automate this process?
 

I have the same issue however I usually round it off to the nearest integer meaning everything else will fall into line as long I don't go beyond or before it. Electronic music can also be more syncopated when you start you using poly-rhythms.
 
You can try using the new Vocal stretch thing (Region FX) as well, however I'm not very sure of the tolerant that is before it starts decimating parts. 

Shift+M will allow you to manually define beats to change the tempo map.
 
Rocky

+1 on the Shift-M thing - it defines the current location as a specific measure/beat.  Best to snap to transients only when going through the song.  It's not automatic, but it doesn't take that long once you get moving on it.  You can decide to do every downbeat, half note, or quarter note, depending on the material.
 
Or, just ask your collaborator what the tempo was.  For all you know, they tapped it in and it isn't even a round number.  Or it wasn't recorded to a click.  You can fiddle all you want, but it's easiest and best to just ask.