It was 2015 when I first began to grapple with tipping when ordering at a counter-service restaurant. I had ordered a fried chicken sandwich at Pine State Biscuits in Portland, Ore., and a friend chided me for not tacking on a gratuity to my credit card payment. I hadn’t even considered it.

“ They’re working hard back there! They’re getting paid so little! "

“ But I’m just ordering at the counter! I always tip waiters well, but this is not a waiter! I’m not a terrible person! ”

I lost the argument, and ended up going back to leave a cash tip.

Turns out, I’m not alone. As small, independently owned cafes, smoothie bars and fast-casual restaurants in the United States have adopted customer-facing touch-screen payment systems in recent years — and as credit cards have replaced cash for even the smallest purchases — Americans and (heaven help them) foreign visitors have been confronted with a new kind of tipping. Point-of-sale systems, with touch screens asking you whether you’d like to tip $1, $2 or $3 for that latte or 15, 20 or 25 percent for a salad, have been spreading like an infectious disease — or an infectious new dance craze, depending on your perspective.

(Tipping via credit card is nonexistent or at least much less common at large chains like McDonald’s and Burger King. Starbucks, though, allows tipping when customers order through their app and managers are free to put out a tip jar, said a spokes woman.)