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	$93.83	6.178%	$99.6268	$99.63	$99.65	$99.60
Purchase #2	$238.85	13.527%	$271.1592	$271.16	$271.15	$271.20
Purchase #3	$122.37	5.292%	$128.8458	$128.85	$128.85	$128.80
Purchase #4	$211.62	10.311%	$233.4401	$233.44	$233.45	$233.40
Purchase #5	$74.46	5.526%	$78.5747	$78.57	$78.55	$78.60
Purchase #6	$108.81	8.549%	$118.1122	$118.11	$118.10	$118.10
Purchase #7	$161.46	4.363%	$168.5045	$168.50	$168.50	$168.50
7 purchase totals =	$1,011.40		$1,098.2633	$1,098.26	$1,098.25	$1,098.20