And that's fine. Tips in club settings are entirely optional (and entirely for "local" bands - if you saw, say, McCoy Tyner in a club, you'd not tip the band) , and usally come when a customer is "reached" by the music to a more-than-normal degree, and/or if "special" requests are made. But if you just have a good time from afar, no expectations are in place, none whatsoever (although most club dates pay such that a little sumpin-sumpin certainly don't hurt anybody, if you know what I mean...)
But if you do tip, make it something useful, or at least something not insulting.