When any tracts, lots, or parcels of land have been included in one assessment and sold for taxes under one decree, the owner or any one entitled to redeem may redeem any lot or part of said property where the part to be redeemed can be ascertained by legal and usual subdivision. It shall be the duty of the tax assessor to ascertain the amount of taxes on such portion desired to be redeemed as provided for under Section 40-10-121.