Verifying files were transferred correctly

How can I check that files made it to S3 without corruption? Is there some checksumming going on within s3sync, and if so how can I get s3sync/cmd to display this, and then compare to a local MD5 or SHA-1 checksum?

Also, is there some way to simply show the size of files (to the exact no. of bytes) on S3? I tried s3fox as well but it just shows KB.

I know S3 is very reliable but I'm just trying to make sure any errors can be caught when sending backup files, particularly during initial testing.