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	$120.95	13.344%	$137.0896	$137.09	$137.10	$137.10
Purchase #2	$47.88	4.741%	$50.15	$50.15	$50.15	$50.20
Purchase #3	$95.87	5.289%	$100.9406	$100.94	$100.95	$100.90
Purchase #4	$37.67	3.185%	$38.8698	$38.87	$38.85	$38.90
Purchase #5	$210.53	8.127%	$227.6398	$227.64	$227.65	$227.60
Purchase #6	$71.88	4.521%	$75.1297	$75.13	$75.15	$75.10
Purchase #7	$30.72	6.492%	$32.7143	$32.71	$32.70	$32.70
7 purchase totals =	$615.50		$662.5338	$662.53	$662.55	$662.50