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	$95.75	9.848%	$105.1795	$105.18	$105.20	$105.20
Purchase #2	$170.31	3.212%	$175.7804	$175.78	$175.80	$175.80
Purchase #3	$111.59	11.527%	$124.453	$124.45	$124.45	$124.50
Purchase #4	$84.89	5.343%	$89.4257	$89.43	$89.45	$89.40
Purchase #5	$191.77	7.222%	$205.6196	$205.62	$205.60	$205.60
Purchase #6	$144.73	4.536%	$151.295	$151.30	$151.30	$151.30
Purchase #7	$125.94	10.452%	$139.1032	$139.10	$139.10	$139.10
7 purchase totals =	$924.98		$990.8564	$990.86	$990.90	$990.90