I'm not sure who told you to go bigger (the company?) but in my experience, you give them your measurements and they make it to those measurements. So keep in mind that if you do not round up, your costume's going to be EXTREMELY FORM FITTING.
For the most part, I just rounded to the nearest whole number for mine. However, even giving myself a few extra centimeters for legs and inseam (so I could have a larger crotch area) it was still pretty tight and uncomfortable. Everything else was pretty good, though.
So I'd just say round up and then.. kind of guess at a semi larger number for the crotch. D;
If you still are confused, email them. More often than not, they're happy to help.
Also, in the future you may get better help by posting this to an actual cosplay forum or something. Just a thought.
Pssst. It's not really trademarked.