So long as you are confident you abide by any relevant laws and consumer rights then you can design the PoS how you like, but having designed a UI for large PoS systems, I know it's a real nightmare area for legal requirements.
Under some (probably many) laws, the consumer must be able to see clear details of the price being charged for each item, along with any surcharges and discounts, and as the items are rung up.
This is to give the customer a fair opportunity to spot any disparities between the price listed on display and the price being rung up before paying for the transaction.
To enable this, and reduce risk of breaking any laws or consumer rights, it's best to provide as much relevant information (context) as possible rather than stripping it to a bare minimum. Providing feedback 'in place' clearly helps reduce confusion.
The concept of switching from one display/tab to another could potentially make it easy for an unscrupulous person to change figures or details as the screen switches, and at the very least, place a seed of doubt in a suspicious person's mind.
Here's a fraction of an example law
THE PEOPLE OF THE STATE OF CALIFORNIA DO ENACT AS FOLLOWS:
SECTION 1. The heading of Article 1 (commencing with Section 13300)
is added to Chapter 13 of Division 5 of the Business and Professions
Code, to read:
Article 1. Point-Of-Sale Displays
SEC. 2. Section 13300 of the Business and Professions Code is
amended to read:
- (a) The operator of a business establishment that uses a point-of-sale system to sell goods or services to consumers shall
ensure that the price of each good or service to be paid by the
consumer is conspicuously displayed to the consumer at the time that
the price is interpreted by the system. In any instance in which the
business advertises a price reduction or discount regarding an item
offered for sale, the checkout system customer indicator shall display
either the discounted price for that item, or alternatively, the
regular price and a credit or reduction of the advertised savings. Any
surcharges and the total value to be charged for the overall
transaction also shall be displayed for the consumer at least once
before the consumer is required to pay for the goods or services. The
checkout system customer indicator shall be so positioned, and the
prices and amounts displayed shall be of a size and form, as to be
easily viewable from a typical and reasonable customer position at
each checkout location.