148.068.  Tax assessed, when, supplemental assessment. — 1.  The amount of tax which is shown to be due on the return, including revisions for mathematical errors, shall be deemed to be assessed on the date of filing of the return including any amended returns showing an increase of tax.  In the case of a return properly filed without the computation of the tax, the tax computed by the director shall be deemed to be assessed on the date when payment is due.  If a notice of deficiency has been mailed, the amount of the deficiency shall be deemed to be assessed sixty days after the notice of deficiency was mailed if no protest is filed; or, if a protest is filed, then upon the later of the date when the determination of the director or the administrative hearing commission becomes final.  Any amount paid as a tax or in respect of a tax shall be deemed to be assessed upon the date of receipt of payment, notwithstanding any other provision of sections 148.010 to 148.110.

  2.  If the mode or time for the assessment of any tax under sections 148.010 to 148.110 including interest, additions to tax, and penalties is not otherwise provided for, the director of revenue may establish the same by regulation.

  3.  The director may, at any time within the period prescribed for assessment, make a supplemental assessment, subject to the provisions of section 148.060 where applicable, whenever it is found that any assessment is imperfect or incomplete in any material aspect.