The advertisement shall also contain a statement that the franchise will be struck off, sold, and awarded to the person, firm, or corporation making the highest cash bid therefor; that at the time of the opening of the bids any responsible person, firm, or corporation present or represented may bid for the franchise or privilege a sum not less than 10 percent above the highest sealed bid therefor, and the bid so made may be raised not less than 10 percent by any other responsible bidder and the bidding may so continue until the franchise is finally struck off, sold, and awarded to the highest bidder therefor in lawful money of the United States.