Some cashiers are busybodies that make comments on your purchases. The majority don't but it can be very upsetting if you do experience it. I had one question me on what I was going to do with pizza dough, which was... weird to say the least, I'd assume that someone would be making pizza with pizza dough. I've had cashiers ask me if food I was buying was good or make comments on new products they havne't seen yet.
When I was a cashier I certainly looked at the products I was scanning beyond orienting to the barcode so I don't really know where you're getting that from. It wasn't "mentally exhausting" or anything either, that's a little weird to say. In fact, cashier are required to actually 'look' at the product in some amount of detail because some items need to be bagged a certain way and they need to check ID on some products, like alcohol.
When I was a cashier I certainly looked at the products I was scanning beyond orienting to the barcode so I don't really know where you're getting that from. It wasn't "mentally exhausting" or anything either, that's a little weird to say. In fact, cashier are required to actually 'look' at the product in some amount of detail because some items need to be bagged a certain way and they need to check ID on some products, like alcohol.