No. You don’t. Your gift voucher can be used across multiple transactions until it expires or until such a time that your balance is $0. To check the balance of your gift vouchers, simply go to My Account (you will be asked to login if you are not currently logged in), go to Gift Vouchers and all your vouchers with their balance and expiry date, will be listed there.
NOTE:. You do not have to be a registered user in order to use your voucher, however you will only need to be registered if you want to see it in my account.