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	$155.54	8.339%	$168.5105	$168.51	$168.50	$168.50
Purchase #2	$247.79	6.641%	$264.2457	$264.25	$264.25	$264.20
Purchase #3	$142.77	6.429%	$151.9487	$151.95	$151.95	$151.90
Purchase #4	$75.79	6.288%	$80.5557	$80.56	$80.55	$80.60
Purchase #5	$142.92	11.509%	$159.3687	$159.37	$159.35	$159.40
Purchase #6	$145.91	9.308%	$159.4913	$159.49	$159.50	$159.50
Purchase #7	$212.71	8.537%	$230.8691	$230.87	$230.85	$230.90
7 purchase totals =	$1,123.43		$1,214.9897	$1,215.00	$1,214.95	$1,215.00