To Run:

ruby sales_tax.rb <FILE_NAME1>

For Help:

ruby sales_tax.rb --help

Assumptions:

An item price must be greater than 0.
An item count must be a whole number.
An input price is for a single item, regardless of the item count.
The line item format will not change. (COUNT_INTEGER + " " + INPUT_NAME_STRING + " at " + PRICE_FLOAT)
The first line of Output 1 has a typo.   There should not be a space between the item and colon.
Each input file contains 1 shopping cart.


Explanation:

A file is opened, and the ShoppingCart module:
  1) Creates a new receipt. 
  2) Processes each line to extract the appropriate parameters needed to create a new Item.
  3) Appends a new Item to the receipt.
  4) Prints the receipt when all lines have been processed.

Upon instantiation, an Item object stores it's name, count, total, and tax values.  Exempt and Imported are subclasses of Item, and ImportedExempt is a subclass of Imported.  Imported overloads Item.name and all the Item subclasses overload Item.tax_rate.

When an item is added to the receipt, the receipt's total & sales_tax values are incremented accordingly. 

BigDecimal is used in the calculations to avoid rounding issues with Floats.  A custom BigDecimal method handles the rounding up of tax.

Exempt items are detected by matching the item name to CSV lists of medical and food words.