In addition to the amount authorized by section 375.16, the county board of St. Louis County may annually appropriate from the county revenue fund a sum not exceeding $5,000 as a contingent fund for use by the chair of the county board, or any member of the county board acting in the capacity of the chair, at the chair’s discretion to pay for incidental costs and expenses incurred in expediting the business of the county of St. Louis. The fund shall be under the exclusive control of the chair of the county board or any member of the county board acting in the capacity of the chair, subject to postaudit by the county board.