If another state or local unit of government has previously assessed an excise tax on the illegal cannabis or controlled substances, the taxpayer must pay the difference between the tax due under section 297D.08 and the tax previously paid. If the tax previously paid to the other state or local unit of government was equal to or greater than the tax due under section 297D.08, no tax is due. The burden is on the taxpayer to show that an excise tax on the illegal cannabis or controlled substances has been paid to another state or local unit of government.