How does GetDiscountPrices with multiple items work?

I know GetDiscountPrices can be called with a single item and it evaluates that by creating a virutal cart with only that item in it and then runs the promo engine against that cart, but how does it work when I pass multiple items?

Let's say I pass the method 25 items, does it create 25 carts and run the engine 25 times, thus taking the same amount of time it would take to just call GetDiscountPrices 25 times with each item?

I ask all this becuase we are trying to speed up our search pages where we show up to 25 items at a time and their prices with discounts.

Thanks,

Brian