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	$144.63	9.619%	$158.542	$158.54	$158.55	$158.50
Purchase #2	$236.89	8.126%	$256.1397	$256.14	$256.15	$256.10
Purchase #3	$85.33	10.304%	$94.1224	$94.12	$94.10	$94.10
Purchase #4	$117.28	4.734%	$122.832	$122.83	$122.85	$122.80
Purchase #5	$156.94	10.491%	$173.4046	$173.40	$173.40	$173.40
Purchase #6	$36.62	10.290%	$40.3882	$40.39	$40.40	$40.40
Purchase #7	$77.80	13.689%	$88.45	$88.45	$88.45	$88.50
7 purchase totals =	$855.49		$933.8789	$933.87	$933.90	$933.80