The sales tax is based on the state you live in, so it should be the same for every purchase if you live in a state that makes Ebay collect it:
https://www.ebay.com/help/buying/pay...=4771#section3
To see the tax you paid on something (I don't think there is a way to see it before you buy, but you can calculate it as (sale price + shipping)*tax rate), you can see the exact amount after you have paid by clicking purchase history --> (on the right of the purchase) view order details --> on the right it shows price, shipping, tax, and total.