Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$20.78	10.261%	$22.9122	$22.91	$22.90	$22.90
Purchase #2	$76.35	13.650%	$86.7718	$86.77	$86.75	$86.80
Purchase #3	$170.62	11.828%	$190.8009	$190.80	$190.80	$190.80
Purchase #4	$215.31	10.856%	$238.6841	$238.68	$238.70	$238.70
Purchase #5	$209.42	6.204%	$222.4124	$222.41	$222.40	$222.40
Purchase #6	$71.36	10.579%	$78.9092	$78.91	$78.90	$78.90
Purchase #7	$169.40	10.857%	$187.7918	$187.79	$187.80	$187.80
7 purchase totals =	$933.24		$1,028.2824	$1,028.27	$1,028.25	$1,028.30