If you are the importer of record, payment to the broker will not relieve you of liability for customs charges (duties, taxes, or other debts owed CBP) in the event the charges are not paid by the broker. Therefore, if you pay by check, customs charges may be paid with a separate check payable to the "U.S. Customs and Border Protection" which will be delivered to CBP by the broker.
19 C.F.R. §111.29