When payment of annual taxes or levies on real estate and tangible personal property, machinery and tools and merchants' capital is not made when due on June 5 and on December 5, a penalty of 10% of the taxes past due shall be assessed on June 6 and December 6 and shall therewith be due and payable in addition to said annual taxes.
Whenever said past due taxes, together with the penalty, have not been paid by the due date, interest at the annual rate of 10% shall begin from the first day after such taxes are due and shall be collected upon the principal and penalties of all taxes then remaining unpaid pursuant to the Code of Virginia.