All bids shall be sealed. At least five bids from responsible vendors, agents, manufacturers or producers shall be invited, and as many more as is practicable. Any bid received subsequent to the specified date and time of bid opening shall be stamped with the time received, rejected and returned to the bidder. Bids shall be tabulated by item number and unit price in such form as to afford a basis for strict comparison of prices at the time and place of opening. Method of award shall be stated in proposal and prices requested shall be net including transportation and delivery charges fully prepaid by the bidder F.O.B. point of destination. Where bids are secured by departments or other agencies all original bids, declinations to bid, copy of specifications, list of those invited to bid, copy of advertisement, if any, with publisher's certificate attached, correspondence and other papers thereto pertaining, including a complete explanation of rejection of lower bids shall be promptly forwarded to the Executive Department, Office of General Services, with all copies of the order, accompanied by a statement, signed by an individual duly authorized to open bids, to the effect that all bids timely received were opened publicly at the time and place specified in the proposal, and that all timely bids received appear on the tabulation.