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	$178.49	6.810%	$190.6452	$190.65	$190.65	$190.60
Purchase #2	$35.75	8.300%	$38.7173	$38.72	$38.70	$38.70
Purchase #3	$99.43	10.433%	$109.8035	$109.80	$109.80	$109.80
Purchase #4	$211.47	7.784%	$227.9308	$227.93	$227.95	$227.90
Purchase #5	$90.45	10.743%	$100.167	$100.17	$100.15	$100.20
Purchase #6	$154.63	4.300%	$161.2791	$161.28	$161.30	$161.30
Purchase #7	$184.72	13.170%	$209.0476	$209.05	$209.05	$209.00
7 purchase totals =	$954.94		$1,037.5905	$1,037.60	$1,037.60	$1,037.50