Each taxpayer shall keep complete and accurate records of taxable sales and of charges, together with a record of the tax collected thereon, and shall keep all invoices, bills of lading and such other pertinent documents in such form as the tax commissioner may by regulation require. Such records and other documents shall be preserved for a period of time not less than three years, unless the tax commissioner shall consent in writing to their destruction within that period or by order require that they be kept longer.