When you thank a cashier, it’s just the standard polite way to close the interaction and you’re not actually expressing gratitude to them for simply doing their job. Responding with “you’re welcome” overstates that transactional exchange and implies a debt that doesn’t exist. It comes across as presumptuous.


BUT that’s not their intent, they’re just mindlessly saying “you’re welcome” because that’s how their manager or grandma or someone taught them to respond. So although I find it mildly annoying, it’s not something I’d ever point out to them.