To sweenten tomatoes sauce and kill some of the acid taste that comes with tomatoes, and they dod have high acid content, that is why they need to be canned by a certain method to makes sure the lids seal and they do not spoil.
Instead of using a teaspoon of White Sugar, grate a small Carrot into the sauce as it cooks. Grate it finely and it will cook into the sauce and add it sweeting effect and not appear in the finished sauce