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	$210.59	5.805%	$222.8147	$222.81	$222.80	$222.80
Purchase #2	$14.92	12.481%	$16.7822	$16.78	$16.80	$16.80
Purchase #3	$98.52	13.555%	$111.8744	$111.87	$111.85	$111.90
Purchase #4	$80.52	10.156%	$88.6976	$88.70	$88.70	$88.70
Purchase #5	$136.34	5.429%	$143.7419	$143.74	$143.75	$143.70
Purchase #6	$66.94	4.697%	$70.0842	$70.08	$70.10	$70.10
Purchase #7	$137.82	10.189%	$151.8625	$151.86	$151.85	$151.90
7 purchase totals =	$745.65		$805.8575	$805.84	$805.85	$805.90