35 ILCS 200/18-140

Extension upon equalized assessment of current levy year. All taxes shall be extended by each county clerk upon the valuation produced by the equalization and assessment of property by the Department for the levy year. In the computation of rates, a fraction of a mill shall be extended as the next higher mill. Rates may be calculated beyond 3 decimal points to allow the extension to be as close to the levy requested as possible. Each installment of taxes shall be extended in a separate column. Installments shall be equal and as to each installment a fraction of a cent shall be extended as one cent.