So tired of all the fighting...

My girls are about 5 and a half years apart in age...but they fight like crazy!! I can not believe how much bickering and arguing about the stupid things they do! I feel like all I say is knock it off to them...we have started just sending them to their rooms when they start (they share a room) for 20 mins. but somedays it feels like they are in there all day! I don't know what else to do, but it is disturbing the entire family...what do you do to stop the bickering between siblings???