Write a program to produce a sales receipt. Each time the user clicks on a button, an item and its price should be read from a pair of text boxes and displayed in a properly aligned list box. Use a class-level variable to track the sum of the prices.

When the user clicks on a second button (after all entries have been made), the program should display the number of items purchased, sum of the prices, the sales tax (assuming an HST of 13% of the total), and the total amount to be paid.