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	$200.74	13.343%	$227.5247	$227.52	$227.50	$227.50
Purchase #2	$129.47	8.193%	$140.0775	$140.08	$140.10	$140.10
Purchase #3	$24.88	6.211%	$26.4253	$26.43	$26.45	$26.40
Purchase #4	$106.26	5.308%	$111.9003	$111.90	$111.90	$111.90
Purchase #5	$151.80	6.403%	$161.5198	$161.52	$161.50	$161.50
Purchase #6	$92.39	13.811%	$105.15	$105.15	$105.15	$105.20
Purchase #7	$170.89	8.330%	$185.1251	$185.13	$185.15	$185.10
7 purchase totals =	$876.43		$957.7227	$957.73	$957.75	$957.70