All contracts, except in cases of emergency, over $5,000 that the commission may let for construction or materials shall be let after public advertising. The commission shall advertise for bids for the work or materials at least ten days prior to the letting of any contracts therefor. The advertisement shall state the place where bidders may examine the plans and specifications and the time and place where bids for the work or materials will be opened. Each bidder shall accompany his bid with a certified check payable to the commission, for a reasonable sum to be fixed by the commission, as a guarantee that if the contract is awarded to him, he will enter into a contract with the commission for doing the work or furnishing the materials. The contract shall be let to the lowest responsible bidder, and the successful bidder shall give bond or other security for the faithful performance of the contract, in such form and amount as the chairman may require. The commission is authorized to reject any and all bids. In the event that all bids are rejected, the commission shall advertise for new bids as in the first instance. All such bids and contracts shall be public records. The commission is authorized, in its discretion, to do any and all such work by force account.