1. For purposes of taxes imposed by sections 143.011 to 143.996, a taxpayer’s method of accounting shall be the same as his method of accounting for federal income tax purposes. If no method of accounting has been regularly used by the taxpayer, taxable income for purposes of sections 143.011 to 143.996 shall be computed under such method that in the opinion of the director of revenue fairly reflects income.

2. If a taxpayer’s method of accounting is changed for federal income tax purposes, his method of accounting for purposes of sections 143.011 to 143.996 shall similarly be changed.