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	$100.52	11.341%	$111.92	$111.92	$111.90	$111.90
Purchase #2	$112.58	10.460%	$124.3559	$124.36	$124.35	$124.40
Purchase #3	$59.32	12.674%	$66.8382	$66.84	$66.85	$66.80
Purchase #4	$184.91	8.484%	$200.5978	$200.60	$200.60	$200.60
Purchase #5	$225.52	7.224%	$241.8116	$241.81	$241.80	$241.80
Purchase #6	$199.60	5.272%	$210.1229	$210.12	$210.10	$210.10
Purchase #7	$17.61	8.832%	$19.1653	$19.17	$19.15	$19.20
7 purchase totals =	$900.06		$974.8117	$974.82	$974.75	$974.80