Yeap. I think the 5% is referring to poly only.
So u shud not have much of a problem entering NUS.
But as for your desired course, it will depend on the no of people fighting for the 'x' no of places. And from there, grades or rather university score shud be taken into account.
The choices (in order of merit) also matter.
If u want Law, i heard u must put it as 1st or at most, 2nd choice to be at least shortlisted for an interview. GP grades matter too. (duh ...)
All the best!