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	$239.47	10.308%	$264.1546	$264.15	$264.15	$264.20
Purchase #2	$6.93	12.195%	$7.7751	$7.78	$7.80	$7.80
Purchase #3	$37.98	5.584%	$40.1008	$40.10	$40.10	$40.10
Purchase #4	$92.27	12.167%	$103.4965	$103.50	$103.50	$103.50
Purchase #5	$236.71	12.737%	$266.8598	$266.86	$266.85	$266.90
Purchase #6	$105.83	5.371%	$111.5141	$111.51	$111.50	$111.50
Purchase #7	$24.87	11.143%	$27.6413	$27.64	$27.65	$27.60
7 purchase totals =	$744.06		$821.5422	$821.54	$821.55	$821.60