nuclear war would inevitably lead to a nuclear holocaust that would cause the near extinction of the human species.
If you use tactical nukes, then it’s not much more significant than using thermobaric ordnance or cassettes or even chemical weapons or anything else kinda nasty and non-conventional.
It won’t lead to a global thermonuclear war and thus a nuclear holocaust any more than use of sarin in Syria did.
However! If you don’t give a flying fuck about a smaller holocaust then I don’t give one about your bigger one even if it involves me, I just don’t care.