There are distinctly American customs and cultures that Europeans would look as stereotypically American.
Also, when asking this, expect a real response back.
A. When they ask how you are, tell them.
Just because they're saying "I'm alright" instead of pouring their heart out about how they had one customer earlier who caused a lot of trouble, doesn't mean that they aren't being honest.
I would never initiate a casual conversation with a cashier. If the cashier asks me how I am today, I'll say "fine, thanks." and that's it.
If some people live in an island where some place are around 10 degrees and other around 15 degrees, they may say "our island is very diverse, look, yesterday I went to the south, and it was freezing! 10 degrees! it's 5 degrees less than here!"
I understand you see the differences in people you meet in your same culture. But how do you even see the similarities, if you have no experience of other cultures?