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	$150.68	13.370%	$170.8259	$170.83	$170.85	$170.80
Purchase #2	$143.60	11.514%	$160.1341	$160.13	$160.15	$160.10
Purchase #3	$112.85	13.593%	$128.1897	$128.19	$128.20	$128.20
Purchase #4	$93.54	8.694%	$101.6724	$101.67	$101.65	$101.70
Purchase #5	$146.45	6.121%	$155.4142	$155.41	$155.40	$155.40
Purchase #6	$228.65	10.687%	$253.0858	$253.09	$253.10	$253.10
Purchase #7	$103.76	7.359%	$111.3957	$111.40	$111.40	$111.40
7 purchase totals =	$979.53		$1,080.7178	$1,080.72	$1,080.75	$1,080.70