Ya, I could estimate sales tax for sure. I just don't have precise records like I do for income tax where I can just look at last year's 1040[1]. Instead I would have to think about how much I spent last year on goods & services subject to sales tax. And I don't even really know what's subject to that and not in some cases tbh. I spend a lot on rent and daycare and other things not subject to sales tax. Really it probably only applies to a relatively small % of my spending personally.

Also not all of sales tax really falls on me. Some % falls on the provider of the goods in the form of lower prices. It depends on the price elasticity of the product in question. Taking this into account would only further complicate the question.

[1] I'm a very precise record keeper of my income taxes now after I screwed something up years ago which cost me $$$. I keep everything in a github repository. It's pretty awesome actually. Highly recommended!