In all books I have read so far (Beekes, for example), it is assumed that the word for hundred in PIE cmtom came from the word for "ten", decm. They thus postulate that the oldest (non-attested) form was dcmtom.
I wonder whether another explanation is also possible. For example why it could not origin from the root com meaning "together" plus a common neuter adjectival suffix -tom? cmtom thus would mean "something put together". Is this explanation possible and if no, why?