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	$51.41	13.211%	$58.2018	$58.20	$58.20	$58.20
Purchase #2	$52.29	6.231%	$55.5482	$55.55	$55.55	$55.50
Purchase #3	$110.76	12.561%	$124.6726	$124.67	$124.65	$124.70
Purchase #4	$35.78	13.178%	$40.4951	$40.50	$40.50	$40.50
Purchase #5	$100.66	11.137%	$111.8705	$111.87	$111.85	$111.90
Purchase #6	$126.74	10.349%	$139.8563	$139.86	$139.85	$139.90
Purchase #7	$148.67	8.612%	$161.4735	$161.47	$161.45	$161.50
7 purchase totals =	$626.31		$692.1180	$692.12	$692.05	$692.20