I've had chickens for about 10 years now... I have never wormed them. Unless you see a need to... like weight loss or such, then you should worm... other than that. It's preference.
Hi, I would watch their droppings for signs of worms. The most common offender is round worms and they are easy to see. A vet can do a fecal sample and tell you if they need worming and what kind. the test isn't costly.