If there is a good seal, N95 will do better than 95% in almost all cases. The 95% is for the maximum penetrating particle size, i.e. the worst case size particle. This is typically about 0.3um. Particles that are larger or smaller than this will be filtered above 95%. If you want to nerd out on filtration theory, https://en.wikipedia.org/wiki/HEPA is a good place to start.