I have created a rule that is discount for sell price; (Rules event: "Calculating the sell price of a product")
Unit base price is 100 EUR. I discounted 10% and I can see the 90EUR on product page and on Shopping Cart page. When I go to Checkout page the price will back to original base price (100 EUR).
And I also created another Rule, that's event is "After saving a new commerce line item" and action is Commerce Line Item -> Multiply the unit price by some amount but there were not changed anything. Actually I just succeed to change unit price of product but total amount had calculated based for base price.
I checked the view of "commerce_cart_form" and "commerce_cart_summary" and unit price fields was formatted amount I changed with other options, I selected "show calculated price" but nothing changed.
Everything is OK on product displays pages and on commerce_cart_form view. After "commerce_cart_summary" view shows base and uncalculated price.