FX Tape Sim produces a lot of aliasing. Check out the
thread cecelius linked to above, where you can find some pictures.
The importance of aliasing is often overstated when people are comparing plugins (if it's 60db or more down nobody's going to notice), but when I tested FX Tape Sim there were aliased components just 6db below the 10KHz test tone. That's loud enough to be audible.
Although FX Tape Sim was the worst of the tape sims we tested, it's certainly not alone when it comes to aliasing. All the cheap and free tape sims exhibited some aliasing. Among the freebies, Bootsie's TesslaPRO was one of the better ones in that regard.
I should add that all of the tests were performed at 44.1KHz. Aliasing should be somewhat less of a problem at 96KHz.