Shopify records which kind every order is. When an order's prices include tax, its line prices, discounts and shipping all contain it; when they exclude tax, every one of those amounts is net, and the tax sits only on Shopify's own tax entries. A report that adds the two kinds together without noticing mixes gross and net figures, and every margin built on top of it is off by the tax rate.
On a nouz statement everything down to the tax line includes tax, and net revenue and everything below it exclude tax. An order whose prices exclude tax is raised to that basis line by line, using the rate Shopify actually charged on each line, so a $100,00 item with $10,00 of sales tax reads as $110,00 of gross revenue, $10,00 of tax and $100,00 of net revenue, exactly like the same item sold at $110,00 with the tax inside. Each order is read on its own basis, so a shop that holds both kinds needs no setting.
The difference matters most when comparing shops or markets. A US store and a German store with the same net prices show different checkout totals and the same net revenue, which is the figure every margin should be measured against. The VAT price calculator converts a price between the two.