paypal standard configuration

[guardiano78]

Hello,
I've to set "paypal standard" as payment method by adding the 4% fixed the order total.
The problem is that when I use paypal as a payment method, the total amount is incorrect.
Let me explain with an example:
Add to cart a product that costs € 5.00 + VAT 22%
Then I choose the shipping method which costs € 8.00 + VAT 22%
so I'm in this situation:
------------------------------------
article1                € 5.00
Shipping costs      € 8.00
Tax                     € 2.86
------------------------------------
order Total           € 15.86

So far everything is correct.
Now I have to select the payment method, then they select PayPal where next is the amount of € 0.63 and also so far everything is correct because the 4% of the order is just € 0.63

after selecting PayPal, a summary of amounts is this:
------------------------------------
article1                 € 5.00
Shipping costs       € 8.00
Tax €. 2.86
Payment costs       € 0.66
------------------------------------
order Total           € 16.52

As you can see under "Payment costs" does not put me € 0.63, but puts € 0.66 and therefore the calculation of the total order is not correct.
In short, there are 3 cents more that there should be !!
So I tried to change the percentage from 4% to 10%, then the list of payments to paypal option, puts me € 1.59 which it is the correct amount; but when I select it as a payment method in total it puts me € 1.76 (ie 17 cents more).

How can I fix?

ps.I attach jpg expenses configuration paypal
use joomla 3.5 and virtuemart 3.0.14

[guardiano78]

I also tested a standard payment method (for example cash on delivery) with the 4% of the costs. The calculation is always wrong. But unlike paypal in subtotal it puts the same price that appears next to the payment description.
I also tried with clean installation of joomla 3.5 and virtuemart 3.0.14

[guardiano78]

I upgraded to virtuemart 3.0.16 and joomla 3.5.1, but I still have this problem.
It's never happened to anyone?
the payment costs should be: (5 + 8 + 2.86) * 4/100 = 0.63
Instead, in the totals, for the calculation of the payment costs goes like this: (5 + 8 + 2.86 + [(5 + 8 + 2.86) * 4/100 = 0.63]) * 4/100 = 0.66
I am sure that the plugin adds the payment costs to the total order and then recalculates the 4%
Even "standard payment" makes this kind of calculation, however, at paypal difference amounts are equal (both in total and in the list of payments)
If it's not a bug, please explain to me what is wrong in my virtuemart configuration?

thanks for your patience!