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	$116.39	3.539%	$120.509	$120.51	$120.50	$120.50
Purchase #2	$46.51	9.373%	$50.8694	$50.87	$50.85	$50.90
Purchase #3	$52.30	10.144%	$57.6053	$57.61	$57.60	$57.60
Purchase #4	$224.25	12.548%	$252.3889	$252.39	$252.40	$252.40
Purchase #5	$56.50	8.406%	$61.2494	$61.25	$61.25	$61.20
Purchase #6	$38.29	6.134%	$40.6387	$40.64	$40.65	$40.60
Purchase #7	$13.47	3.122%	$13.8905	$13.89	$13.90	$13.90
7 purchase totals =	$547.71		$597.1512	$597.16	$597.15	$597.10