The cashier's getting paid the same. If they were like waitstaff that get paid by the customer, it'd be a shitty thing to do, but for folk that are hourly/waged, it's still not nice, but not quite shitty territory, since you're not messing with their income, just time (and as someone that's worked customer support, I'd rather count pennies for 2 hours than deal with another irate "I'm angry because I can't read" ahole)