Prepayment; precomputed loan transactions.

If the entire unpaid balance outstanding on a precomputed loan transaction is paid by cash, renewal or otherwise, at any time prior to maturity, the lender shall give a refund or credit of the unearned portion of such charge, according to the rule commonly known as "the rule of 78th" ["the rule of 78's"], which refund or credit shall represent at least as great a portion of the original charge as the sum of the consecutive monthly balances of the contract scheduled to be outstanding after the date of prepayment bears to the sum of all the consecutive monthly balances of the contract scheduled to be outstanding under the schedule of payments in the original instrument or instruments evidencing the loan; provided however, that if the contract is prepaid in cash rather than renewed or refinanced, the lender shall not be required to make a refund or credit, if the amount, computed as herein set forth, would be less than one dollar ($1.00) for each loan paid prior to the maturity.