Any amounts borrowed by a county as provided in the preceding section shall not exceed 85 percent of the total of taxes levied for all purposes on said county’s tax roll for the next preceding fiscal year, and at no time during the year for which borrowed shall the unpaid total of the amounts so borrowed as shown by the auditor’s accounts at the close of any month be allowed to remain at more than 85 percent of the uncollected balance of taxes for the current year as shown by said accounts.