CtA318- I think that your boxing routine would be a fine form of HIIT. If you keep your intensity high for the entire round, you should get a great workout. Actually, it might be hard to finish all of those rounds at near 100% intensity.
My initial thought is that 3 minute rounds may be a little too long for maximum intensity, even though 3 min. rounds are standard in boxing. Someone else may be able to advise on that better than me.