For the privilege of selling tangible personal property at retail, a tax is imposed upon all retailers in the city at the rate of 0.875 percent from July 1, 1956 to and including June 30, 1968; to impose a 0.900 percent tax on or after July 1, 1968 to and including June 30, 1969; to impose a 0.925 percent tax on or after July 1, 1969 to and including June 30, 1970; to impose a 0.950 percent tax on or after July 1, 1970 to and including September 30, 1984; and to impose a 0.975 percent tax on or after October 1, 1984 and each and every year thereafter of the gross receipts of the retailer from the sale of all tangible personal property sold at retail in the city. (Ord. 1587 NCS §2, 1984; Ord. 891 NCS §2; Ord. 619 NCS §§2-4; Ord. 444 NCS §4; prior code §23.8(a)(1).)