Petty cash is a small amount of discretionary funds in the form of cash used for expenditures where it is not sensible to make any disbursement by cheque, because of the inconvenience and costs of writing, signing, and then cashing the cheque.
The most common way of accounting for petty cash expenditures is to use the imprest system. The initial fund would be created by issuing a cheque for the desired amount. An amount of $100 would typically be sufficient for most small business needs as the expenses to be covered are for small amounts. The bookkeeping entry for this initial fund would be to debit Petty Cash and credit bank account.
As expenditures are made, the custodian of the fund will reimburse employees and receive a petty cash voucher with a receipt/invoice attached in return. At any given time, the total of cash on hand plus reimbursed vouchers must equal the original fund.
When the fund gets low, e.g. $20 remaining, the custodian (a bookkeeper or a member of the administration staff) requests a top up and submits the vouchers for reimbursement. Assuming the vouchers add up to $80, an $80 top up cheque is issued and an $80 debit towards office expenses is recorded. Once the cheque is cashed, the custodian again has cash at the original amount of $100.