There's no standard tip amounts. It's up to you. I would say, if the girl is nice, don't be cheap like the ancient Viet dudes who tip $1. C'mon old dudes! That works out to 50 cents per boob, LOL!
Some of the girls working coffee are pretty cool. When you find one you like, its good to tip her more.
There's a few shops in the area staffed with unfriendly girls. I'd be surprised if those girls get any tip at all, LOL.
