Only you can decide if you should race or not. Sensible advice would be to pull out, recover and race next time. There are always more races and you should put your health first. Right thats sensible out the way. Most of us have raced with a niggle and as long as it doesn't get worse during the race you should be okay. If it does deteriorate then I would recommend stopping. It's meant to be fun not agony. Regarding taper I would take the week off completely from running and cycling to rest the niggle. Have a couple of easy swims but focus on rest. You won't lose fitness and the rest will do you more good.