Most of the time i'll say yes just on principle, and same for tips. If I leave a cash tip and the server asks if I need change then I'll always say yes, it comes across that they just assume that I'm going to leave something for them (which almost exclusively I will, but again it's on principle). Left a $50 bill to pay for a $12 meal once and they asked if I needed change...uh, yeah, i'm gonna need change. I leave better tips when they don't ask the question, and especially if they bring back exact change.