Bonds issued hereunder shall be sold at public sale, after advertisement of the sale in a newspaper having general circulation in the State or in a financial publication published in the city of New York or, in the discretion of the municipal council, in both such publications. Such advertisement shall appear not less than ten days prior to the occasion set for such sale. The bonds may be disposed of at private sale if there are no bids received or if all bids are rejected. The provisions of this section shall not prevent a sale at private sale to the United States or any agency thereof.