Unfortunately, this mini-processor chops the tomatoes very fine, bordering on pureeing them. I actually used this to make a spectacular gazpacho with tomatoes, peppers and cucumbers from my garden. It did prepare that very well. But if you're looking for something that would be used more in a salsa or guacamole, I don't think this mini-processor would work for you.
I know when I was trying to make salsa the tomato came out not pureed but only slightly chunky. This was fine for me since I don't want something too chunky but if you want bigger chunks, you're better off hand chopping them or using something else.
If you pulse the food processor it will chop tomatoes. But, why do you want your tomatoes to come into contact with the plastic? I only use my Mini-Prep FP for dicing onions, garlic, tumeric or ginger really small. I would never use it for processing acid foods like tomatoes than may possibly leach the plasticizers out of the FP into my food.