Brian writes: My wife and I ask for cash back at the grocery store. Unlike an A.T.M., a cashier can give you small bills. I request $40 and ask that it be broken up into one $20, one $10, one $5 and five $1s. My wife requests $39, getting small bills without having to ask. Whose method is best?

I have bad news: You are both terrible. I suppose asking for $39 is slightly more onerous to the brain and hands of your cashier. But generally, it’s best to avoid throwing curveballs at service workers; it’s confusing, distracting and makes an already-medium-to-low-fun job harder. I share your frustration with A.T.M.s that spit only 20s. I think there was once an A.T.M. near SoHo that gave coins, but perhaps that was merely a beautiful dream. Use small bills to tip service workers, not as a reason to make them do your wallet homework. Find a local business you like and break your bills there instead.