I'm not familiar with the tipping system in the US. One day I'm buying a coffee and i am presented with a machine asking me to tip 15%, 18% and 20% and no tip. I feel like I have to tip at least 15% but i still haven't tasted the coffee and I won't even sit down at the place. I don't mind tipping if I get some sort of service.
What do people do with the tipping for getting a to-go coffee?