Purchase of bonds, when

Provided it can be shown to be to the financial advantage of the county, whenever there are any moneys on deposit in the sinking fund in excess of the amount needed for the redemption of any bonds then matured or required to be redeemed, the director of finance of each county, with the approval of the governing body, may buy with those moneys, on the open market, any of the outstanding bonds or any interest bearing notes of the county, or invest the moneys in obligations of, or obligations unconditionally guaranteed by, the United States of America or in savings accounts, time deposits, or certificates of deposit of any bank or trust company, within or without the State, to the extent that the savings accounts, time deposits, or certificates of deposit are collaterally secured by a pledge of obligations of, or obligations unconditionally guaranteed by, the United States of America; or in obligations of any state of the United States of America or any agency, instrumentality or local government of any such state, the provision for payment of the principal of and interest on which shall have irrevocably been made by deposit of obligations of, or obligations unconditionally guaranteed by, the United States of America. All bonds and notes purchased pursuant to this section shall be canceled and not reissued.