Whenever a person engages in business both within and outside the city, the tax imposed by this chapter for those businesses using gross receipts or cost of operations as a taxing measure shall be based on business activity that is fairly apportioned to reflect that portion of business initiated, conducted, rendered or delivered from within or to the city. Guidelines for apportionment may be issued from time to time by the tax collector. (Ord. 1921 NCS §2 (part), 1993.)