>> hw028
  Amount due is    59.22:
  Insert a bill such as 1, 5, 10, 20, 50, or 100: 20
  Amount due is    39.22:
  Insert a bill such as 1, 5, 10, 20, 50, or 100: 20
  Amount due is    19.22:
  Insert a bill such as 1, 5, 10, 20, 50, or 100: 10
  Amount due is     9.22:
  Insert a bill such as 1, 5, 10, 20, 50, or 100: 10
  $   60.00 paid
  $   59.22 groceries
  $    0.78 change back