In the cart's total block «Total for everything» there are two toggles that change the way the cost is counted — urgent order and combined calculation.
Urgent order
The «Urgent order» toggle counts the order as urgent. When it is on, the cost is recalculated with urgency taken into account by the firm's rules (urgent production is usually more expensive). The toggle is always available.
Combined calculation
The «Combined calculation» toggle turns on an alternative way of counting the order cost. It applies when the firm has such a calculation option configured, and may give a different total compared to the usual one. If the firm does not use combined calculation, the toggle is not shown.
Both toggles recalculate the total at once. How the total sum is made up — in the article «Cart contents and total cost».