Receipt amount and discount rules

This is how the register calculates amounts:

There are two functions, applyAmountRule(amount) and applyDiscountAmountRule(discountAmount).

The amount rule function does this:

Convert the amount to pennies by multiplying by 100.0

If the fractional part is less than 0.001 then take the floor amount else take the ceiling amount.

This amount is multiplied by 0.01 and returned.

The discount amount rule does this:

Convert the amount to pennies by multiplying by 100.0

If the fractional part is greater than 0.999 then take the ceiling amount else take the floor amount.

This amount is multiplied by 0.01 and returned.

So the amount rule always goes up unless it is within 0.001 of a penny.

The discount rule always go down unless it is within 0.999 of a penny.

Discounts are calculated with fractional amounts during the calculation of modifier amounts, line amounts and the subtotal.

The amount rule is applied to each modifier, each line in the receipt, the full price of the receipt, the subtotal, the tax, the alcohol tax, the credit card fee, and the service fee. All of these amounts go up unless they are within 0.001 of a penny.

The full amount does not have any discounts and the subtotal does have discounts applied.

The final discount is calculated as the full amount - subtotal and then the discount rule is applied to this result. The discounts always go down unless they are within 0.999 of a penny.

There is one exception to these rules. If the menu has tax included in the price then the discount rule is used in all calculations. This is so items for example set to $7.00 don't end up being $7.01

Cash Discounting Fee

Credit card fee from a given amount. You want to add the credit card to an amount. Do this:

fee = ( amount / ( 1.0 - percentage ) ) - amount

fee = applyAmountRule(fee)

Credit card fee included in an amount. Given the total amount you want to know how much of it is the fee. Do this:

fee = amount * percentage

fee = applyAmountRule(fee)