The county auditors shall not be required to assess on the taxable property of their counties or of any town, city or incorporated village or school district therein, for any purpose, nor for all purposes added together, any rate of taxation containing or resulting in any fraction other than a decimal fraction, nor in any fraction less than one-tenth of a mill; but if the sum required to be raised for any or all purposes results in a fraction less than one-tenth of a mill such fraction shall be dropped.