Yes the WP eStore plugin has coupon configuration option:
here is a page that lists the main features of eStore
I have tried to keep the eStore simple to use but it’s a little bit more complex than the simple shopping cart since it has a lot more functionality and stuff. this video tutorial should give you more insight:
http://www.tipsandtricks-hq.com/ecommerce/wp-estore-quick-setup-and-usage-video-tutorial-593