Most merchants get charged all their credit card processing fees at the first of the month following the month when the transactions took place. Credit Card deposits each day match their cash register daily credit card deposit summary. At the end of the month the deposits on their merchant account monthly statement match exactly their bank statement. This is called Monthly Discount.
Sometimes a merchant is charged their discount rate with every transaction, called Daily Discount. For example, if the merchant received a $100 transaction and their discount rate was 3% and $.30, then they would receive a deposit of $96.70, $3.00 for the 3% plus the transaction fee of $.30. The next transaction could be also $100 but with a different discount rate, this time, of 2.6% and $.30 for a net deposit of $97.10. This is a bookkeeping nightmare! Imagine if there were 50 transactions in the day and they all had different rates. It would be nearly impossible to reconcile with the cash register or your bank account statement!
Occasionally there are merchants who run their bank account tight and do not want a big deposit coming out on the first of each month. However, compared to the nightmare of reconciliation, I would suggest a merchant choose monthly discount and simply keep a balance to cover the estimated fees.