The use of the petty cash account shall be restricted to miscellaneous petty or emergency expenditures, refunds legally payable by an agency, and for cash change to be used in the transaction of the agency's official business. All expenditures made from petty cash shall be charged to an existing appropriation for such purpose, except expenditures chargeable against funds for which no appropriation is required by law. All expenditures or refunds made from petty cash shall be reimbursed out of and charged to the proper appropriation or fund at the close of each month and such other times as may be necessary.