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	$160.61	6.414%	$170.9115	$170.91	$170.90	$170.90
Purchase #2	$161.71	9.829%	$177.6045	$177.60	$177.60	$177.60
Purchase #3	$106.60	10.160%	$117.4306	$117.43	$117.45	$117.40
Purchase #4	$225.94	10.609%	$249.91	$249.91	$249.90	$249.90
Purchase #5	$144.82	13.165%	$163.8856	$163.89	$163.90	$163.90
Purchase #6	$203.53	3.735%	$211.1318	$211.13	$211.15	$211.10
Purchase #7	$97.31	8.779%	$105.8528	$105.85	$105.85	$105.90
7 purchase totals =	$1,100.52		$1,196.7268	$1,196.72	$1,196.75	$1,196.70