As a cashier myself, this is so true. I say no problem all the time, and no one else has a problem. You sound just as nice when you say "no problem" vs. "youre welcome" ; Agreed, I say "No problem" to people all the time.
Pirates didn't wear eyepatches because they were blind. They were them to keep one eye acclimated to the dark at all times. At night, they would switch the patch to the other eye and have perfect night vision.