For purposes of subsections (2) and (3) of section 77-5804, the taxpayer shall be deemed to have paid indirectly any state sales or use taxes paid by a contractor on building materials annexed to an improvement to real estate built for the taxpayer. The contractor shall certify to the taxpayer the amount of the state sales and use taxes paid on the building materials, or the taxpayer, with the permission of the Tax Commissioner and a certification from the contractor that state sales and use taxes were paid on all building materials, may presume that forty percent of the cost of the improvement was for building materials annexed to real estate on which the tax was paid.