how to create rules in Medusa Nextjs?

[rapid hare]

I want to create custom rules in medusa. For example if someone buy $100 above then they will get 5% discount.

[calm shale]

nextjs-starter-medusa as his name say is a starter so you can do whatever you want with it
Algorithmically speaking I think you can do that in the cart, when the customer adds products in the cart you can create a hook that will calculate the price of the products when added together with a condition so if it's over 100$ he gets 5% discount