AWS S3 multi-tenancy billing

I have a multi tenancy (java web app) that store/transfer files using AWS S3. Our customers are paying us for: - Storage - Data transfer

The calc of storage is very simple and it's ok for now, but my problem is calculate data transfer of our customers, this envolve partial download problems, etc.

I wan't know about your experience with this approach.

There's a way to explore this costs in a effective way?

For example: I send tenant-id and user-id on getObjectRequest. If there's a way to get this data is ok.

Anyone have a better idea to deal with that?