Individual attributes discount

Hi all,
ive read through a couple of different topics related to this but havent been able to find the exact problem that i have, what i'm trying to do is put on different discounts for different attributes in an item

The site is a furniture store and they need the prices to reflect their realworld prices, so when they take an item, such as a 3 piece suite with a 3 seater, 2 seater and an armchair, they deduct 15% off the range, but round up or down, to make a nice tidy figure, so the actual discount on the 3 items might be 15.45%, 14.87% 15.9% in order to round everything off

What this leaves me with is on the website, the 3 items set as attributes with their original prices, and when i give a 15% discount to the item as a whole, a wide variation in prices from their real world prices, as we're dealing with items priced at between 1-2k this makes a difference of a few dollars, it might seem small, but they want the prices reflected online and in the realworld to be the exact same

Any suggestions on how i can give individual discounts to individual attributes?

Thanks in advance, and im gonna keep reading through more topics similar in the mean time in hopes of finding my solution!