~nakereba narimasen – It’s not right not to do something (have to do)
~nakute mo ii desu – It’s fine not to do something (do not have to do)

To use these, you have to change the the verbs to negative (ie. (tomeru)tomenai, kaku(kakanai), miru(minai))

You have to stop the car – Kuruma o tomenakereba narimasen
You don’t have to stop the car – Kuruma o tomenakute mo ii desu

Other Example
Q : Bōshi o (kaburu)kaburanakereba narimasen ka?
A : Hai, bōshi o kaburanakereba narimasen (Positive Answer)
A : Iie, bōshi o kaburanakute mo ii desu (Negative Answer)
Meaning : Bōshi (Cap), Kaburu (Wear/Put On)

Q : Kimono o (kiru)kinakute mo ii desu ka?
A : Hai, Kimono o kinakute mo ii desu (Positive Answer)
A : Iie, Kimono o kinakereba narimasen (Negative Answer)
Meaning : Kimono (Japanese Tradisional Wear), Kiru (Wear)