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	$63.50	3.791%	$65.9073	$65.91	$65.90	$65.90
Purchase #2	$132.74	10.648%	$146.8742	$146.87	$146.85	$146.90
Purchase #3	$237.87	13.310%	$269.5305	$269.53	$269.55	$269.50
Purchase #4	$139.68	6.326%	$148.5162	$148.52	$148.50	$148.50
Purchase #5	$44.27	13.344%	$50.1774	$50.18	$50.20	$50.20
Purchase #6	$232.28	5.298%	$244.5862	$244.59	$244.60	$244.60
Purchase #7	$163.55	4.666%	$171.1812	$171.18	$171.20	$171.20
7 purchase totals =	$1,013.89		$1,096.7730	$1,096.78	$1,096.80	$1,096.80