Section 20. The holder of a retail installment sale agreement may, if the agreement so provides, collect a delinquency and collection charge on each installment in default for a period of not less than fifteen days in an amount not in excess of five percent of each installment or five dollars, whichever is less, and assess and collect a charge, not to exceed ten dollars, for any check, draft or order for the payment of money submitted in accordance with said agreement which is returned unpaid or not honored by a bank or other depository.