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	$59.78	6.137%	$63.4487	$63.45	$63.45	$63.40
Purchase #2	$19.29	10.425%	$21.301	$21.30	$21.30	$21.30
Purchase #3	$194.34	7.700%	$209.3042	$209.30	$209.30	$209.30
Purchase #4	$158.81	11.750%	$177.4702	$177.47	$177.45	$177.50
Purchase #5	$46.77	7.399%	$50.2305	$50.23	$50.25	$50.20
Purchase #6	$76.48	8.362%	$82.8753	$82.88	$82.90	$82.90
Purchase #7	$30.70	12.655%	$34.5851	$34.59	$34.60	$34.60
7 purchase totals =	$586.17		$639.2150	$639.22	$639.25	$639.20