You can see the store rates by clicking 'See all donation rates' on the store page.
If you have installed Give as you Live and want to check the donation rates for your purchase, just click the "Store info" link, found on the right hand side of the bar.
Each store chooses how much commission they pay for a purchase (remember it is Give as you Live that turns it into a donation for your chosen charity!) therefore the donation rates can vary from store to store.
In addition, some stores donate a different amount depending on what product you buy and terms and conditions may apply.