Explanation
According to the B2B Commerce Developer Guide, the ICart interface provides access to the cart object and its related data. The Details property of the ICart interface returns an ICartDetails object, which contains information about the cart such as the currency, the subtotal, the shipping cost, the tax, and the grand total. The Fields property of the ICartDetails interface returns a map of field names and values for the cart object.
Therefore, to get the grand total amount for items in the cart and in the currency of the cart, a developer should use the expression {ICart.Details.Fields.grandTotal}, which returns the value of the grandTotal field from the cart object. References: B2B Commerce Developer Guide, ICart Interface, ICartDetails Interface