Vouchers on Subtotal and not on first price

[Farawyr]

Hello everyone. 

This my first time in asking your help and maybe my question will be really simple for someone that had my same problem.

 

I'm settingin an ecommerce that will give the customers (that are agents, so basically is a B2B) tha chance to set a cumulative discount.
The general discount we are going to make is 40%. Then there will be 5%, a second 5% and a third 5%.

Let's make an example.

I spend 100€, then I apply the 40% so NOW my total 60€.

After this I can add another 5%, which brings my price to 57€.

Now, if I put 40% plus another voucher of 5% on prestashop, my total is 100€ - 40€ - 10€ because he calculates the 5% on the ORIGINAL price, which is 100€, while I need it to calculate on the partial total, which is 60€ after the first discount.

 

Is there anybody that had my same issue? How did you manage to solve it?

 

Thanks