It's the same for Norway, all information is public. It does lead to salaries reaching some sort of equilibrium for the the same role, as it is much harder to argue against an employee, when he points out all his peers are making more money for the same work.
No. Tax information is public in anonymized form. That is different from wages, and the effect is absolutely not the same as if you knew exactly what your peers are making.
I'm trying to encourage talking wages at work, and have gotten my division to disclose theirs, but there's a lot of "oh, but it could lead to discontentment" in the rest of the company. And if you know Norwegians, being mildly at unease is the worst thing that can happen.