If the firm works with VAT, the amount with tax is shown next to the sums in the calculation. This is display only — the tax is not part of the base prices but is added on top for clarity.
When it is shown
VAT is shown if the firm has a tax rate set and its display in the calculation is enabled. If the tax is not configured or its display is off, the sums are shown without VAT.
How it is counted
VAT is counted as a percentage of the sum by the set rate, and then added to it: sum + VAT = sum with tax. The tax is shown both at the section subtotals (materials, services, goods, processing) and at the overall total «Total for everything».
How the sum itself is made up — in the article «Cart contents and total cost».