If you have an exam (flight test or ground exam) to do - then please work out TAS accurately - what you do once you have the licence is up to you - except that be aware that TAS is typically required for flight plans - not IAS....
BTW If you correct IAS to CAS then TAS It willl be more than 3 kts normally - more like 4-6 - why? Because most a/c have a 1-3kt error in the IAS to start with - check the POH.