It's not quite 100%, the merchant has costs associated with using cash: The time a cashier has to spend counting the cash register's content, time spent on bank

It's not quite 100%, the merchant has costs associated with using cash: The time a cashier has to spend counting the cash register's content, time spent on bank runs to put away earnings/get extra coins for change, some fees associated with it, some amount that gets "lost"... I remember the cost was less than credit cards take, but not much lower than Girocard payments.