Well they wouldn't run away, but other than that, yes.
Unless you are using that money to pay for something, they can't take it. Just like a cashier at publix can't take money from someone unless it's for purchase. Companies want to take as much money as they can through credit and they certainly aren't going to have a special "Teebin's 5K" drawer
Basically, if you take money from a customer/guest behind a counter without it being used as payment, it could be considered theft or bribery.