I usually don’t use sugar at all in tomato sauce, I would only use at most a teaspoon for a 500g can of tomatoes if the acidity was really off and I never needed more to get it right. I also don’t think I’ve ever tasted a sauce that I wouldn’t eat if I didn’t add sugar to it. Maybe my tomatoes are less acidic than most, maybe I like the acidity, maybe it’s the amount of onion I add to the sauce, I don’t know, but I could certainly get by without sugar at all.
That said, I honestly still add sugar to my sauce even after I went keto if I feel it needs it. I don’t make tomato sauce nearly as much since I don’t eat pasta anymore, but even if I did I wouldn’t be too concerned. One teaspoon is how much? 5g? And I’m eating at most 1/3 of that, probably less. A full teaspoon is also the high mark of what I’ll use. The point isn’t to taste the sugar, it’s just to blunt the edge of the acidity ever so slightly if it’s a tad too sharp but usually I don’t need any at all.
I have heard that you could use a pinch of baking soda (not baking powder) if your sauce is too sour. I have never tried that myself so I can’t vouch for it.