Every person engaged in the business as defined in section 144.010 of this chapter in this state shall keep such records and books as may be required by title 26, the United States Code, for federal income tax purposes. Such books and records and other papers and documents shall, at all times during business hours of the day, be subject to inspection by the director of revenue or his duly authorized agents and employees. Such books and records shall be preserved for a period of at least three years, unless the director of revenue, in writing, authorized their destruction or disposal at any earlier date.