Discount on wallet topups

We would like to create a discount when users add a certain amount of funds to their wallets.

For example, a user adds $50 to the wallet but will be credited with $55.

How would we go about setting this up?
There will be 6 different tiers for the discounts:

Spend $50 get $55
Spend $100 get $110
Spend $200 get $220
Spend $500 get $550
Spend $1000 get $1100
Spend $2000 get $2200