When I am interacting with someone who is "serving" me in some way and they ask how I am doing... I almost always ask them back. It is quite interesting the different reactions I get. They pretty much have to be pleasant and I think it throws them off when people are pleasant by choice.
this is kind of a jerk thing to do because a server / cashier person basically has to be nice even if they feel crappy so when you ask them "how are you doing" you are forcing them to lie.
But cashiers/servers probably get asked that same question "how are you?" a hundred times per day. Customers who think they are being nice by starting small talk may have the opposite affect. It's all context really.Small talk in a busy line is probably not the best idea.
It all depends on the person, and there's no way to tell without asking. If someone doesn't want to talk, it's quite easy to tell from their response to the question. If that's the case, you end the conversation there, and nobody cares.
Anecdotally, I have started many conversations with service people this way, and I'm not much of a talker. In fact, it's usually them telling me about how horribly things are going, and I just listen. It's interesting how often a perfect stranger will open up to you if you just show a little empathy.
It varies a bit by culture and establishment. I've run into plenty of coffee shop employees from non-chain stores who'll be happy to complain about their day if you inquire. Also got an unexpectedly long answer at a Trader Joe's checkout counter once, a whole story about a messed-up delivery resulting in a bunch of broken bottles, when I asked how he was doing.
