A round off on beam does not receive a deduction. I competed it in level 7, and I got around in the 35's the whole season.
To be specific, you are required to have a flight skill in your routine. It could be in or out of your series. Flight is any skill that you get fully off the beam in a flip. But of course, it needs to be no more than a B skill in level 7. The flight skill area is worth .5 of your SV. So if you do not have your flight skill, you will have a 9.5 SV. Also, the flight skill area is in the same area as the series, so if you do not connect your series, and you do not get your flight, then your start value is still just a 9.5.
Flight skills can be back handsprings, front handsprings, and round offs. All of those skills are B's and receive the same judging and scores as the other flight skills.
The reason most people choose back handsprings over round offs and front handsprings is because of the fact that round offs and front handsprings lead to less skills, and back handsprings are very important in higher level gymnastics such as levels 9 and 10.
Hope this helped!