Any or all bids may be rejected, and the sale may be advertised anew, in the same manner, or the bonds or any portion thereof may thereafter be sold at private sale to any one or more of such bidders, or other persons, by popular subscription or otherwise. In case of private sales, the said bonds shall be sold upon terms not less favorable to the public than the most favorable bid made by a bona fide and responsible bidder at the last advertised sale.