During topup tax is wrong calculated and also on paypal page currency label is display

Assumption : Paypal configuration already done.

Steps to reproduce:

1. Create a customer with CAD currency
2. Now create a one Refill product with 10 USD Price
3. Now admin side create tax on > Configuration > Taxes > Amount : 13.64, Rate (%) : 25.73
4. Now assign above tax to customer
5. Now go to customer login > Services > Topup
6. Now select refill product and check total tax, amount with tax
7. Now make a payment through paypal by click on pay with paypal button
8. Now check topup amount total and their currency on paypal payment gateway page

Expected Result :

1. Tax Total should be correct calculated for different currency and correct total should be display for Amount with tax.

2. On paypal payment gateway page only USD currency should be display before amount. Need to remove currency label. Because here CAD amount is converted into USD currency.

Actual Result :

1. Tax Total and amount with tax is wrong calculated and wrong display.

2. On paypal payment gateway page CAD currency is display after total topup amount and alse $ currency is display before amount. Actually here currency is converted in USD.

Note: Amount should converted based on currency rates running, Make sure currency conversation should working fine for different currency