In preparing said assessor’s book, each county assessor shall provide therein three columns for values. The first to contain the total assessed valuation of tangible personal property assessed to each individual, and the assessed valuation of each tract of land or town lot listed; the second column to contain the valuation of such property as corrected and equalized by the county board; and upon the receipt of a certificate from the state tax commission setting forth the action of said commission in respect to his county, the county clerk shall extend in the third column the valuation as equalized and assessed by said state tax commission. In all cases of extension where the equalized valuation shall happen to be fractional, the clerk shall reject all such fractions as may fall below fifty cents; fractions of fifty cents or more shall be extended as one dollar. The state, county and all other taxes shall be computed and extended by the county clerk in separate columns against the valuation produced by the equalization of the several classes of property by the state tax commission; provided, that only one column shall be used for the total state taxes, and one column for the total county taxes, such columns to be headed with the total tax rate for such purposes, except that the county road tax may be extended in a separate column. In the extension of taxes the fraction of a cent shall be extended as one cent. The county clerk shall add up the figures showing the amount of such tax, in the proper columns, and the aggregate amount in each column shall be noted on each page. Said clerk shall test the accuracy of such additions by computing the amount of such tax on the aggregate amount of property on each page, that he may be certain that the tax has been correctly extended and added.