Coupon Codes For Specific Product Categories & Tags

Hey guys

Just wondering if there was any way to set coupon codes that only work on a specific product category or tag.

For instance I want to reduce a further 10% off my products that feature the "Sale" product tag for 24 hours, but the only way for me to do this at the moment (that I know of) is to manually go in and take 10% off each item then put it to it's original price after the 24 hours.

Any help would be greatly appreciated