I'd really like to see an example that doesn't work, as I haven't been able to break it.
If my math is right, 5 decimal places will give you a sample-accurate stretch up to a stretched length of about 7.5 minutes (based on 44.1kHz). Above that, you'll need 6 decimals, and that will cover you up to 75 minutes (coincidentally right around CD-length), and 7 decimals will get you up to 12.5 hours (another factor of 10)!
Of course, I haven't tested anything above the 7.5 minute mark to see if SONAR will process more than 5 decimals. I would think it should, but I don't want to think about how long it will take to process a stretch that long!