"Is the transaction fee percentage for the various different plans based on the wholesale price I am paying to the supplier or the entire transaction which would be the retail price the customer is paying, including the tax and shipping?"
The order service fee is applied to the cost of the items in your order, not including the shipping or any other charges.
If you have an order with
1 item that cost you $50,
and your customer paid $100 for it,
and you're paying $7.50 for shipping,
and your plan service fee is 5%, the order service fee would be $2.50.
It would be calculated as "item cost total * fee percentage coefficient = order service fee," or "$50 * 0.05 = $2.50."