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	$87.35	6.364%	$92.909	$92.91	$92.90	$92.90
Purchase #2	$142.25	12.491%	$160.0184	$160.02	$160.00	$160.00
Purchase #3	$174.85	9.149%	$190.847	$190.85	$190.85	$190.80
Purchase #4	$71.79	8.195%	$77.6732	$77.67	$77.65	$77.70
Purchase #5	$60.89	3.132%	$62.7971	$62.80	$62.80	$62.80
Purchase #6	$136.25	4.548%	$142.4467	$142.45	$142.45	$142.40
Purchase #7	$48.93	7.466%	$52.5831	$52.58	$52.60	$52.60
7 purchase totals =	$722.31		$779.2745	$779.28	$779.25	$779.20