How can I create eGift cards based on a purchase amount i.e. $15 egift card for every$75 purchase?

[ATLBeautySupply]

I'm having trouble creating gift cards based on the customer's purchase amount. For example, if the customer makes a $75 purchase give them a $15 gift for a designated future use.

[VanKalkerFarms]

There is not a way to automatically give out egift cards with a set purchase value.