There are two things going on here: (1) Actual acidity (the actual acid content that causes indigestion) and (2) Perceived acidity - the taste in your mouth.
Catch-22: Both acid and sugar enhance the tomato flavor in a tomato sauce. Using something like baking soda to chemically neutralize the actual acid content will, as auntdot noted, "dull" the flavor. Jabbur's idea of using a touch of Hershey's Syrup is not without merit as I found out after a little investigating ... it's made from Dutch Processed chocolate (chocolate treated with an alkaline), which is about as alkaline as baking soda (pH=8), so it should work chemically as an acid neutralizer.
Urmaniac13's "sofritto" will not chemically reduce the actual acid content but will balance the flavors. The carrots do not add a "sugary" sweetness like table sugar ... just a flavor balance. Ironically ... if you don't want to use carrots, dark brown sugar is a better option than refined white table sugar because the molasses contains some flavor components found in tomatoes.
How to Reduce The Acid in the Beginning: The majority of the acid in a tomato is in the juice and jelly surrounding the seeds. So, cutting a tomato in half and squeezing out the seeds and jelly (aka "seeding") a tomato reduces the acidity by about 2/3 - it's not just to get rid of the seeds. But, this is not without consequences ... the jelly and seeds also contain flavors that will be lost if discarded before cooking.
In the end: Acidity can be reduced in the sauce but it will be at the expense of flavor. To preserve the flavor - perhaps an antacid prior to eating might be the solution?
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain