(a) As soon as practicable after any return is filed, the department shall examine it. If the return shows a greater tax due than the amount of the remittance sent with such return, the department shall forthwith assess the difference. Such difference shall be paid to the department within ten days after notice of its assessment. If so paid, there shall be no interest or penalty; if not so paid, there shall be added to such amount five per centum thereof and, in addition, interest at the rate of one-half of one per centum per month for each month or fraction thereof from the date of such notice to the date of payment. No taxpayer shall have any right of appeal from such an assessment.

(b) If the department determines that any return or returns of any taxpayer understates the amount of tax due, the department shall assess the proper amount and shall determine the difference between the amount of tax shown in the return and the amount assessed, such difference being hereafter sometimes referred to as the “deficiency.” Such deficiency shall be paid to the department within ten days after a notice of the assessment thereof shall be mailed to the taxpayer by the department. In such case, if such understatement of the tax in the return or returns was made in good faith, there shall be no interest or penalty because of such understatement: Provided, That the deficiency be paid or notice of an intention to file a petition for a reassessment or to appear and be heard, as herein provided, shall be given within ten days after notice of the assessment of such deficiency be mailed to the taxpayer. If such payment is not made within ten days and if no notice of an intention to file a petition for a reassessment or to appear and be heard is given to the department within ten days, as herein provided, there shall be added to the amount of the deficiency five per centum thereof and, in addition, interest at the rate of one-half of one per centum per month for each month or fraction thereof from the date of such notice to the date of payment. If any understatement in any of such returns is false or fraudulent with intent to evade the tax, the deficiency resulting from such understatement shall be doubled and, in addition thereto, an additional one-half of one per centum of such doubled deficiency shall be added for each such month or fraction of a month from the date the tax was originally due to the date of payment.

(c) If the amount of the tax as assessed by the department shall be less than the amount already paid by the taxpayer, the department shall so notify the taxpayer and the amount so overpaid may be taken by such taxpayer as a credit on the tax shown as due in any subsequent return or returns filed in accordance with the provisions of this act.