Can drug screen tell 10 mg oxycodone from 5 mg?

Nope, absolutely not. OxyContin (OC and OP) as well as Roxicodone contain the active ingredient or chemical that produces therapeutic effects called Oxycodone.

A drug screen itself, unless you are required to bring your medications with you, may specifically test for Oxycodone or just opiates in general, however, there is a separate test to test for oxycodone itself.

If a positive result is returned, then the specimen will typically be sent to a laboratory for a gas chromatography/mass spectrometry exam which may be able to detect the different active ingredients, but I seriously doubt that they would do that. It is just to confirm if there is a false positive or false-negative.