Where a person owes to the Commissioner tax, interest, or penalty and the person pays to the Commissioner or the Commissioner recovers some but not all of the amounts owed by the person, the amounts shall be treated as reducing the person’s obligations to pay –

(a) interest, penalty and tax owed under this Act; and

(b) interest, penalty and tax owed under the Central Sales Tax Act, 1956 (74 of 1956); in the above order.