[Chihuahuas] Puppy Biting

[Karen]

I need some advice.  I have a Chihuahua for the first time and am having
trouble with an annoying habit he (Taco) has of ALWAYS nipping and
biting when he is being petted.  I have always had dogs, but never a
chi.  I don't remember this being a huge issue with my other dogs.  Any
advice on how to break this. Taco is nearly 5 month old.  Thanks!!!