User Activity

I have completed the various tax rates by province and indicated on my preferences "Yes" to charging sales tax but eBay has yet to collect tax on any of my sales. What am I not doing right?
If I have 10 items listed for sale and a buyer selects 3 items to purchase at the same time, can the eBay syatem be programmed to calculate a 15% discount of the additional purchases (or the total purchase)?
I've completed the sales tax tables on BOTH eBay and PayPay. Does that mean my customers who use Pay Pal will be charged sales tax twice?