The petty cash voucher is basically a requisition form to keep track of any moneys taken from the petty cash is later supported by a supporting voucher. For example, if a purchase for R(£) 57 is to be made, you may hand R(£) 60 to a person, if you do not have sufficient change in the petty cash, to the person sent to purchase and collect the goods. When the person returns, he / she must hand a slip or supporting source document to the value of R(£) 57 and R(£) 3 change to the petty cashier. When designing a petty cash voucher, you need to look at your own requirements to note any additional information, such as the amount handed to a person, the signature, etc.
Depending on the frequency and amounts involved and the provisions in Tax legislation (Income Tax and VAT (if you are registered for VAT) or any other legislation), a petty cash voucher my not be sufficient to support expenses and Input VAT claimed.