(1) As soon as practicable after the return is filed, the commissioner shall examine it, if it then appears that the correct amount of tax is greater or less than that shown in the return, the tax shall be recomputed. If the amount already paid exceeds that which should have been paid on the basis of the return so recomputed, the excess so paid shall be credited or refunded to the taxpayer in accordance with the provisions of this chapter.

(2) If the amount already paid is less than the amount which should have been paid, the difference, together with interest thereon at the rate of one-half of one percent (½ of 1%) per month from the time the tax was due, shall be paid within sixty (60) days upon written notice and demand by the commissioner. The department, for good reason shown, may waive all or any part of the interest imposed pursuant to this subsection.

(3) If any part of the deficiency is due to negligence or intentional disregard to authorized rules and regulations with knowledge thereof but without intent to defraud, there shall be added as damages ten percent (10%) of the total amount of the deficiency in the tax, and interest in such a case shall be collected at the rate of one percent (1%) per month on the amount of such deficiency in the tax from the time it was due, which interest and damages shall become due and payable upon notice and demand by the commissioner and such executor shall be liable to the estate personally and on his official bond, if any, for any damages accruing under the above provisions through his negligence or willful neglect.