Can I leave feedback once for an order of multiple items?

[nge9831-kgjwxqdxlu]

I often purchase 20-30 stamps in one order. Can I leave one feedback for the whole order or do I have to do it 20-30 times, once for each item?

[disneyshopper]

Regardless of how many feedbacks you leave for a member during the same week, ebay only advances your trading partner's feedback by one feedback.