Order checkout/_summary information in a sensible manner
Remove unnecessary Shipment#persist_cost method
Remove update_attributes_without_callbacks
Only show shipping total on an order if the total is > 0
Calculate default tax using line_item's amount, not total

Total is the amount of the line item + the adjustments
Order adjustment totals comprise of the line items adjustments, the shipments adjustments and the adjustments for the order
Create tax rate after transitioning from address

Whereas previously this was only done before the payment step. It's really surprising to go from the address step and see your product that's 5.99 is now suddenly taxed.

Therefore we apply taxes after address AND before payment, which is the least surprising behaviour
Update an item's adjustments immediately after an adjustment is created.

This way, the adjustment total is updated correctly to reflect the latest changes.
Use real adjustments in order_mailer_spec
Remove useless test for scopes in adjustment_spec
Only call ItemAdjustments if an adjustment has an adjustable

Useful in certain test cases where we don't have an adjustable
Update + persist totals when order transitions from any state that's not cart to any state that's not confirm or complete