Apple Store is 1mi/$
Apple iTunes is 3mi/$

I have gotten several strange amounts awarded when I bought iTunes (i.e. 112 miles instead of 80 miles the last time).

As for the returns, I think if you return the item after the miles have posted, they don't deduct the miles. At least, that is my experience. Perhaps they have the type of software that many stores employ to track people who make a lot of returns, but the three times I have returned something after the miles posted, no adjustments were made.