My wife gives horseback riding lessons; not a job that people typically offer tips for. She's very good at what she does and sometimes a new parent (it's almost always tween girls taking riding lessons) will tip her when they realize how much their kids enjoyed the session. She used to refuse, but after realizing that just made everyone feel awkward, she takes the cash now. However, while she appreciates the gesture, it still makes her feel a little weird.

A simple "thank you, you're awesome" would probably do just as well.

Americans can be deeply sensitive to people thinking they're poor and in need of assistance. And five bucks is practically nothing. Most people might well just take it to Starbucks anyway.