[mjrube94]

I usually do both. I make sure it's at least 15%, then round up. So for example, a $17 delivery would be $19.55 with a 15% tip, so I round up to 20. Depending on the exact amount, it can end up being much more than 15-20%, but still only a few dollars. I always remind myself what it was like being 17-18 years old, trying to save money for gas, movies, etc., and so don't feel bad about giving them a bit more...