As far as I know SoundFont does not support Round Robin. True Round Robin will cycle through different samples when playing the same note even at precisely the same velocity. However if you have enough velocity samples you will achieve pretty much the same effect with live playing with SoundFont, given that its unlikely you will hit the same note with exactly the same velocity over and over. The more velocity layers the better the chance of not hitting the exact same 0-127 velocity.
If you are converting say an SFZ file that has Round Robin sampling you could assign the different RR samples to velocities that are only a few steps apart. So if it had say C4 sampled 4 times for velocities 100 to 111 you could assign RR1 sample to 100, 101, 102 and 103 RR2 to 104, 105, 106 and 107 etc. Or alternatively mix it up with RR1 at 100, RR2 at 101 and so on. It would be a bit of work but is achievable.
I actually tried this with a bass SoundFont I had and it did work. But honestly I couldn't tell much difference between the version that had 4 times the number of samples with RR compared to the smaller version.
