Some ATMs track the serial numbers of the bills you get. Even then, though, it's more private than a card. Unless they have video of you shoving the bills into a machine for payment, say at Walmart self-checkout, they really don't know how many hands the bills passed through before they passed through a reader again. Also, good if you can get a store to break the large bills for you. Then, they only know that you paid for a pack of gum with a 100-dollar bill.