Yes, open your rotate tool settings (double click on rotate tool) and near the top there should be a snap setting that you can input the degree, by default I think it is 90. You can also hold down 'j' to temporarily activate the snap function (or if it is on, it will temp disable it). Hope that helps. You have provided really useful information regarding snaps rotations... It will really help all members out here who are into Maya...So thanks for sharing it here...