The commissioner may grant, upon written request, a reasonable extension of time for filing returns, declarations, or other documents required under state revenue laws whenever, in the reasonable exercise of his judgment, a good cause for the extension exists. The commissioner shall keep a record of every extension granted and the reason for the extension. No extension or extensions, except as otherwise expressly provided by law, shall aggregate more than six months, nor shall any extension of time for filing returns operate to delay the payment of a tax unless a bond satisfactory to the commissioner is posted. In no event shall the commissioner extend the time of filing returns which are required to be filed with the tax receiver or tax commissioner.