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	$39.72	3.864%	$41.2548	$41.25	$41.25	$41.30
Purchase #2	$173.72	9.405%	$190.0584	$190.06	$190.05	$190.10
Purchase #3	$155.83	4.826%	$163.3504	$163.35	$163.35	$163.40
Purchase #4	$225.87	4.390%	$235.7857	$235.79	$235.80	$235.80
Purchase #5	$64.69	10.762%	$71.6519	$71.65	$71.65	$71.70
Purchase #6	$128.28	13.134%	$145.1283	$145.13	$145.15	$145.10
Purchase #7	$225.99	5.365%	$238.1144	$238.11	$238.10	$238.10
7 purchase totals =	$1,014.10		$1,085.3439	$1,085.34	$1,085.35	$1,085.50