subtotal, grandtotal, taxes, discounts

[bcardarella]

• subtotal: should be what total current does
• optional taxes should be taken into account
• optional discount / promo codes should be taken into account
• grandTotal should be the result of subtotal + taxes - discounts

[movstox]

@bcardarella would something like this work http://jsbin.com/tureza/8/edit?html,js,console,output as candidate for pull request