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	$52.73	4.551%	$55.1297	$55.13	$55.15	$55.10
Purchase #2	$68.59	8.828%	$74.6451	$74.65	$74.65	$74.60
Purchase #3	$55.44	8.120%	$59.9417	$59.94	$59.95	$59.90
Purchase #4	$45.53	12.341%	$51.1489	$51.15	$51.15	$51.10
Purchase #5	$54.61	11.197%	$60.7247	$60.72	$60.70	$60.70
Purchase #6	$81.35	10.519%	$89.9072	$89.91	$89.90	$89.90
Purchase #7	$132.60	9.719%	$145.4874	$145.49	$145.50	$145.50
7 purchase totals =	$490.85		$536.9847	$536.99	$537.00	$536.80