Set a target profit or margin — we'll suggest the listing price that hits it after every fee the calculator models.
Sales tax is paid by the buyer on top of your price and never comes out of your profit. Etsy, Depop, eBay, FB Marketplace, Grailed, Whatnot, Reverb charge some of their fees on it, so there a sales tax rate raises the suggested price. "Show tax in the buyer total" changes the buyer total only.
California note: the dropdown shows base and a commonly-cited minimum combined reference (7.25%). Use the exact local rate for the item's destination in the "Sales tax (%)" field if needed.