The department may, upon application made to it in such form as it shall prescribe, on or prior to the last day for filing any report and upon proper cause shown, grant to the association required to file such report, an extension of not more than sixty (60) days within which such report may be filed, but the amount of tax due shall, in such cases, nevertheless, be subject to interest from the due date and at the rate fixed by this act.
72 P.S. § 3420-25