I don't know whether it's a general rule, but in Boston when I was there many years ago it was supposed that the car in the circle has right-of-way over a car entering the circle. It was only of academic interest, as driving in Boston was largely a matter of "who bluffs best." Any attempt to observe a "requirement" to yield to anyone would generally leave one immobile - sometimes for several days. Right of way was determined solely by the rule that he who first admits he saw the other vehicle must yield.

In the US, or other places where one drives on the right side of the road, you make a right turn going in or going out of the circle, so there's never a need to cross a lane of "competing traffic." I should suppose that where you drive on the left your turns would be to the left for the same reason?

John