Notwithstanding any provision to the contrary, the board, with the approval of the Director of General Services, shall, pursuant to this section, fix the rate of interest to be paid by the districts on the sums apportioned during that fiscal year. Beginning each fiscal year the board shall compute the average of the rates of interest which the state pays upon the state school reconstruction and replacement bonds, sold at the three sales of state school reconstruction and replacement bonds occurring immediately prior to that fiscal year, or, if the board so determines, at all of the sales of the bonds occurring in the two years immediately prior thereto, giving effect to the price at which the state school reconstruction and replacement bonds sold at the sales, and the premium, if any paid, thereon. If an apportionment is made prior to the sale of state school reconstruction and replacement bonds, the board shall use the computed average rate of interest which the state paid on the last sale of state school building bonds. The average rate shall be adjusted to the next highest one-tenth of 1 percent to cover the cost of sale and issuance of the bonds and costs of administration. The adjusted average rate shall be the rate paid by districts on apportionments received during that fiscal year, and shall be compounded annually through the 30th day of June of each year.