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	$206.63	10.142%	$227.5864	$227.59	$227.60	$227.60
Purchase #2	$243.70	12.747%	$274.7644	$274.76	$274.75	$274.80
Purchase #3	$179.60	11.633%	$200.4929	$200.49	$200.50	$200.50
Purchase #4	$230.76	6.566%	$245.9117	$245.91	$245.90	$245.90
Purchase #5	$132.75	9.295%	$145.0891	$145.09	$145.10	$145.10
Purchase #6	$175.76	8.594%	$190.8648	$190.86	$190.85	$190.90
Purchase #7	$88.62	12.668%	$99.8464	$99.85	$99.85	$99.80
7 purchase totals =	$1,257.82		$1,384.5557	$1,384.55	$1,384.55	$1,384.60