It is difficult to grate tomatoes as it will easily slip off the hand and wound the hand. Generally tomatoes are pureed by blanching and peeling the skin. Pureeing the tomatoes in a mixie is another way. Coming to the interesting, tricky part....
To get a smooth tomato puree without the skin, I use this method. Certain gravy dishes will taste unique when pureed in this method.The pictures are self explanatory, yet a quick narration for amateurs.
Make a small cut , like a "+" or "x" on the smooth end of the tomato, using a knife. Hold the tomato on the stem end and grate using a grater. The skin stays back and an awesome puree is ready. You can apply this method when 1 or 2 tomatoes are used for a dish.
Half the tomatoes and grate through your palm. The skin stays back without wounding your hand.