The sugar in this recipe is used to balance the acidity of the canned tomatoes. Some canned tomatoes will need very little sugar. If you use San Marzano tomatoes, you may not need the sugar at all. Some off-brand tomatoes will require more than 1/2 teaspoon of sugar. When you finish cooking the sauce, taste it, and if there is still some bitterness to it, add a little more sugar.