Whenever there shall be on hand in any bond and interest fund an amount in excess of the amount which will be required for expenditure therefrom within the then next succeeding twelve months, the governing authorities of the municipality may use such excess amount to purchase the outstanding bonds of such municipality which are payable from such fund whenever, in the judgment of the governing authorities, the best interest of the municipality would be served thereby. When such bonds are purchased, they shall be cancelled and retired and shall not thereafter be resold or reissued.