Price and discount calculation in microservices

I would like to ask about your ideas for pricing in microservices architecture.

Let's assume that the product has its standard price, which may be lower depending on whether the client is business or individual, whether there is a promotion for a given product and what conditions a given promotion has. For example, 30% discount promotion if there are> 3 products from the "A" category in the cart.

As you can see, the price can be lowered depending on many conditions.

Knowing this and that our data is in many databases - how to approach the calculation of the current price for a given customer?

Do you have an idea, design patterns?

Thanks in advance!