Credit is Cheaper Than Cash

My place of work, like many places, has a pair of vending machines in the break room. They recently put credit / debit card readers on the machines in addition to the bill and coin feeds. I just today realized that if you use a credit card to buy something, it's cheaper. Like 85 cents for a pop with cash, 50 cents with card. I assume it's significantly cheaper for the vending company to not have to come out and empty the machine.