menos mal ( at least ) se los ( it ) di ( give ) a un taxista ( a taxi driver )
entonces, el objeto directo es el taxista y "se" es el objeto indirecto de la oración
objeto directo: persona de quien se habla
objeto indirecto : lo que se hace por esa persona
so basicly, here when you say "se los" you are saying that you gave "them" (those things - dollars, pennies?- ), to somebody. se refers to the thing that you do for the person in your sentence!
hope it help, out!