Notwithstanding the provisions of § 399, § 541 and § 544 of this Title 62, incorporated cities, towns or municipalities possessing sinking funds may, when authorized so to do by the lawfully constituted governing body of such city, town or municipality, invest such sinking funds, when such funds are not required for the payment or purchase of bonds, in bonds of the United States, bonds of the State of Oklahoma or in any type of interest or dividend-bearing account in a sum covered by the terms of the Federal Deposit Insurance Corporation, or The Federal Savings and Loan Insurance Corporation. Providing further, that any interest or dividends accruing to the benefit of an incorporated city, town or municipality from the investment of such sinking funds may be credited to the general fund of such city, town or municipality.