I DO TOO and I DON'T EITHER

Use too with a positive sentence:

A: I like chocolate.
B: I like chocolate too!

Use either instead of too when the verb is negated:

A: I don't like chocolate.
B: I don't like chocolate either!

A: I've never liked chocolate.
B: I've never liked chocolate either!

Notice that the form of tag questions also depends on verbal negation:

I like chocolate, don't I?
I don't like chocolate, do I?