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	$37.47	8.673%	$40.7198	$40.72	$40.70	$40.70
Purchase #2	$166.62	12.413%	$187.3025	$187.30	$187.30	$187.30
Purchase #3	$134.81	10.244%	$148.6199	$148.62	$148.60	$148.60
Purchase #4	$130.65	9.527%	$143.097	$143.10	$143.10	$143.10
Purchase #5	$194.88	10.261%	$214.8766	$214.88	$214.90	$214.90
Purchase #6	$165.42	4.580%	$172.9962	$173.00	$173.00	$173.00
Purchase #7	$116.90	11.583%	$130.4405	$130.44	$130.45	$130.40
7 purchase totals =	$946.75		$1,038.0525	$1,038.06	$1,038.05	$1,038.00