Vouchers and scirra store questions

Hello,

I was participating in the amazon July 2015 promo and now I have 100$ value vouchers

I have a few questions:

1. Can I pay the 25$ seller fee with those vouchers?

2. If i want to buy only a product valued at 5$ and I use the vouchers, after the purchase will I have vouchers valued at 95$, or I must buy of more that 100$ at once in order to not lose vouchers value?

Thanks