You will want to find Sergeant Rehban to turn in your Taris Commendations as an Empire player. Sergeant Rehban is located in the first outpost you come across upon landing on the planet. Keep in mind that Sergeant Rehban is a Equipment Commendations vendor as there are no Weapon Commendation vendors for Taris Commendations that I can point you in the direction of... This is the best bang for your buck.
If you have already left Taris and still want to turn in your commendations there is yet another option... At the Imperial Fleet there is another NPC that accepts Taris Commendations, his name is Sergeant Opelan. A picture of him is below.