Discount for total amount… is it possible?

Hi,

I need to sell my photos and give discount as the quantity increases. So the client can have a discount for choosing to buy a higher quantity of photos.

i.e. the regular price for one photo is U$ 10. If the client decide to buy 3 photos, the total amount will be U$ 27 (the unit price goes to U$ 9, a 10% discount). If the client decide to buy 6 photos, the total amount goes to U$ 48 (unit price goes to U$ 8, a 20% discount from original price)

Is it possible to do it using Image Store?

Thanks