If sufficient funds are not collected to retire outstanding certificates of indebtedness issued wholly or in part against revenues that consist of uncollected taxes within two months after their due date, there must be set aside monthly from current tax collections, exclusive of tax levies dedicated to the payment of principal of and interest on outstanding evidences of indebtedness, not less than ten percent of the amount of the collections until the past due certificates have been paid.
N.D.C.C. § 21-02-08