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.
do you feel better now?
do you feel better now?
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.