The problem doesn't have anything to do with burning a CD. The OP probably just noticed the silence while listening to the CD, but it was already there before being handed to Nero.
The solution is to not leave it up to SONAR to determine where your song ends, but rather to explicitly specify the endpoint yourself. This is a good practice for other reasons, too, such as heading off the opposite problem: truncating a file prematurely and chopping off reverb tails at the end. It will also take care of leading silence from a count-in.
By default, SONAR determines the end-of-song based on the location of the last event in the project. That isn't always reliable, because it may not be apparent (to you) where that last event is, or even what it is. It could be a MIDI note, an automation node, or a leftover from a long clip you'd imported and subsequently truncated. An "event" is anything in the project that affects playback, and many events aren't even visible.
What you want to do is set markers at the start of the song and at the end of the song. Then, before exporting, select all tracks from the first marker to the last marker. That will assure that the export contains exactly what you want, no more and no less. There will be no need to edit the exported file before burning to a CD, and every subsequent re-export will be identical to the last.
I've long advocated for this to be an automatic feature in SONAR, the ability to designate markers as the start-of-song or end-of-song. It could be implemented easily without having to rewrite a lot of code or compromise backward compatibility. But until that happens, you'll have to do it yourself.