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	$55.25	9.299%	$60.3877	$60.39	$60.40	$60.40
Purchase #2	$99.78	11.372%	$111.127	$111.13	$111.15	$111.10
Purchase #3	$133.85	5.215%	$140.8303	$140.83	$140.85	$140.80
Purchase #4	$139.67	11.335%	$155.5016	$155.50	$155.50	$155.50
Purchase #5	$224.28	12.458%	$252.2208	$252.22	$252.20	$252.20
Purchase #6	$104.89	7.482%	$112.7379	$112.74	$112.75	$112.70
Purchase #7	$62.97	4.406%	$65.7445	$65.74	$65.75	$65.70
7 purchase totals =	$820.69		$898.5498	$898.55	$898.60	$898.40