Let me get this straight. Are you asking if the gift card balance can be used to pay for the cost of the item, plus any shipping costs that's attached to that item? Yes, if that is what you are asking.
Here is an example:
An item on eBay is selling for $5.00 + $3.00 shipping. With this gift card, after deducting the $8.00, you would be left with a new gift card balance of $2.00.