It depends a lot on the card type, the location, the volume of the business and it’s risk profile, but eventually can get to a pricing scheme called interchange+, which is a fixed fee (generally <15¢) on top of the cost to process cards for your provider (so fee from the issuing bank + network fee).
In the US this varies a LOT depending on the card type, but most consumer cards are approx 1% interchange + a small fixed fee. In Europe these interchange rates are regulated at 0,3% for consumer cards. There are cases of special schemes (eg. CB in France) where processing can be even cheaper.
These algorithms are trivial to implement for big companies. Google (in YouTube) and Microsoft (in Cortana) have similar things, it's likely Apple uses a custom-made version as well.
To answer the previous question, I'd assume part of their revenue comes from big music labels: knowing what songs are about to go big (before anybody else realizes it), from where their popularity originates, and lot more, is invaluable for them.
In the US this varies a LOT depending on the card type, but most consumer cards are approx 1% interchange + a small fixed fee. In Europe these interchange rates are regulated at 0,3% for consumer cards. There are cases of special schemes (eg. CB in France) where processing can be even cheaper.