On a percentage basis that's true, but if the transaction is small, such as a $3 coffee, then the actual debit fee is (($3 x 0.05%) + $0.21) ~= $0.22, but Squar

On a percentage basis that's true, but if the transaction is small, such as a $3 coffee, then the actual debit fee is (($3 x 0.05%) + $0.21) ~= $0.22, but Square would only charge $0.0825 in fees. I suspect those losses add up at the transaction volume that Square sees.