A.R.S. § 42-18114

A real property tax lien shall be sold pursuant to this article to the person who pays the whole amount of delinquent taxes, interest, penalties and charges due on the property, and who in addition offers to accept the lowest rate of interest on the amount so paid to redeem the property from the sale, which may not exceed the rate prescribed by, and computed pursuant to, section 42-18053. The lien bears interest at the bid rate from the first day of the month following the purchase of the tax lien.