Any such city, holding a certificate of purchase at tax sale, may, at its option, pay any unpaid taxes due the county and purchase from the county any tax sale certificate held by the county on the same real estate, making payment in the event of such purchase of the amount which would then be required to redeem from sale to the county or any lesser amount which the county may be lawfully enabled to accept. All amounts so paid shall be entered in the tax sale records of such city and added to the amount required to redeem from sale. All amounts so paid shall be payable out of the general fund.