- buy a pack of gum with a counterfeit $100, get 98 real dollars back
- even with legit currency, it can throw off the drawer. Business might have a policy for cashiers to never have more than, say, $200 in the drawer. Force half of that to be your $100, and now the cashier has crippled change-making ability. Business have this policy to make them less tempting to rob and limit the damage if they are.
It’s easy for a cart of groceries to come out to $200 these days; how do these businesses accept cash in the first place?
It was not uncommon for someone to show up with their paycheck to do their weekly shopping, handing it over to the cashier and taking the rest in change. The amount of cash that worked through a busy grocery store must have been pretty amazing.
I’m sure the exact policy adopted, if any, depends on a number of factors such as how often cash is used and typical purchase size.