Is it possible to apply coupon code based discount to cart items only?

Currently when customer enters a discount code in cart or in checkout, he can then go back to the website and see lots of products discounted.
Our client doesn't want that. Is there a way to avoid it?

Coupon that applies to order total is almost the answer, but we need a discount to specific product category for example. So we can't use this solution always.

What would be the best way to approach this?

EDIT: Better put, we need a way to limit coupon code discounts to cart/checkout price calculations only.

Regards,
Stepan

It has nothing to do with the "coupon code".  The behavior is due to the use of Discount Type "Assigned to products".
You can try using type "Assigned to subtotal", with a Requirement rule like "Has one product". (But note that if you use a %, it will apply to entire subtotal, not just the product).

New York wrote:
Thanks for the quick response. I tried that, but it doesn't cover all our use cases.
The client creates huge coupon discounts for large amounts of products, but not for all of them. He usually uses percentage instead of totals etc.
I worry I will have to make quite some changes to NopCommerce itself then :(

RE:  "make quite some changes to NopCommerce itself "
I recommend you create a plugin.
If you can't handle your cases with a Discount Requirement rule, then you can create a plugin to override service methods.