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	$235.83	6.695%	$251.6188	$251.62	$251.60	$251.60
Purchase #2	$100.32	10.784%	$111.1385	$111.14	$111.15	$111.10
Purchase #3	$129.86	5.234%	$136.6569	$136.66	$136.65	$136.70
Purchase #4	$95.55	10.188%	$105.2846	$105.28	$105.30	$105.30
Purchase #5	$61.91	7.731%	$66.6963	$66.70	$66.70	$66.70
Purchase #6	$64.35	13.628%	$73.1196	$73.12	$73.10	$73.10
Purchase #7	$39.83	8.570%	$43.2434	$43.24	$43.25	$43.20
7 purchase totals =	$727.65		$787.7581	$787.76	$787.75	$787.70