>This scene hints that the cashier's analytical skills are >next to none and this alone explains why she is a cashier.
Her numerical analytics skills perhaps, but she might be great at something else. Maybe she is a poet, or a musician, or great at handling 5 kids, or something else that you are terrible at.
Just something that doesn't pay well, so she has to be a cashier.
This is kind of a form of Moravec's paradox: we assume what is easy for us must be easy for others, and what is hard for us must be also hard for others too.
I can't find the reference right now, but this was a famous problem in early testing of monkey's intelligence. They showed the monkey's pictures of humans and they couldn't distinguish them, so it was assumed they were fairly dumb. But then eventually someone figured out they were much better at distinguishing pictures of other monkeys.
Of course it's still possible that the cashier is not good at anything, but in my experience that's very rare. Most people have some skills.