All bids received pursuant to a public sale shall be opened in public on a date and at a time and place to be specified in the notice of sale. Bonds sold at public sale shall be awarded to the bidder offering to purchase the bonds at the lowest interest cost to the issuing unit calculated in the manner established by the Secretary of the Commission in the notice of sale. (1931, c. 60, s. 18; 1935, c. 356, s. 1; 1939, c. 231, s. 3; 1971, c. 780, s. 1; 2005-238, s. 8.)