(1) If, upon examination of a return made under the provisions of this chapter, it appears that the correct amount of tax is greater or less than that shown in the return, the tax shall be recomputed. Any overpayment of tax so determined shall be credited or refunded to the taxpayer. If the correct amount of tax is greater than that shown in the return of the taxpayer, the commissioner shall make his assessment of additional tax due by mail or by personal delivery of the assessment to the taxpayer, which assessment shall constitute notice and demand for payment. The taxpayer shall be given a period of sixty (60) days from the date the commissioner mailed or hand delivered the notice in which to pay the additional tax due, including penalty and interest as provided in this section, and if the sum is not paid within the sixty-day period, the commissioner shall proceed to collect it under the provisions of Sections 27-13-29 through 27-13-41, provided that within the sixty-day period the taxpayer may appeal to the Board of Review as provided by law.

(2) In the case of an overpayment of tax, interest shall be computed under the provisions of Section 27-7-315. In the case of an underpayment of tax, interest at the rate of one percent (1%) per month, except as otherwise provided in this subsection, from the due date of the return may be added or assessed in addition to the additional tax due as provided in subsection (1) of this section. For taxes assessed by the commissioner on or after January 1, 2015, the rate of any interest assessed under this section shall be:

(a) Nine-tenths of one percent (9/1 of 1%) per month for such taxes assessed on or after January 1, 2015, and before January 1, 2016;

(b) Eight-tenths of one percent (8/1 of 1%) per month for such taxes assessed on or after January 1, 2016, and before January 1, 2017;

(c) Seven-tenths of one percent (7/1 of 1%) per month for such taxes assessed on or after January 1, 2017, and before January 1, 2018;

(d) Six-tenths of one percent (6/1 of 1%) per month for such taxes assessed on or after January 1, 2018, and before January 1, 2019; and

(e) One-half of one percent (½ of 1%) per month for such taxes assessed on or after January 1, 2019.

(3) In case of failure to pay any additional taxes as assessed under this section, unless it is shown that the failure is due to reasonable cause and not due to willful neglect, there may be added to the additional amount assessed a penalty of one-half of one percent (½ of 1%) of the amount of the additional tax if the failure is for not more than one (1) month, with an additional one-half of one percent (½ of 1%) for each additional month or fraction thereof during which the failure continues, not to exceed twenty-five percent (25%) in the aggregate.