According to what you said, you would better to choose sunglasses with angular and geometric frames or rectangular and horizontal styles. Do not get sunglasses that have small frames. In general, you should select frames with straight or angular lines that will help make the face look thinner and longer to sharpen a round face. retro sunglasses, wayfarer sunglasses, wraparound sunglasses are nice choices, which are quite classic and can flatter various kind of people.
Theoretically, we choose our eye glasses according to our face shape instead of our head. If your face is round, you should avoid round sunglasses. If you face is square, you can try round sunglasses. As your head is round, if your face is not too square, you'd better select a pair of square sunglasses. They will balance your head and make it look better.
Sunglasses are very popular accessories for people to flatter their appearance. Their functions are far beyond the protection in recent year. You must find many people wear sunglasses even not in sunny day. Choosing suitable sunglasses can make look much better. If you have a round head, you must avoid round sunglasses. Sunglasses with square frame can make you look good. The shape of square frame can balance the circle of your head and face.