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	$132.97	6.479%	$141.5851	$141.59	$141.60	$141.60
Purchase #2	$165.74	6.857%	$177.1048	$177.10	$177.10	$177.10
Purchase #3	$81.97	10.847%	$90.8613	$90.86	$90.85	$90.90
Purchase #4	$93.71	7.637%	$100.8666	$100.87	$100.85	$100.90
Purchase #5	$129.45	10.554%	$143.1122	$143.11	$143.10	$143.10
Purchase #6	$228.57	10.851%	$253.3721	$253.37	$253.35	$253.40
Purchase #7	$48.79	4.263%	$50.8699	$50.87	$50.85	$50.90
7 purchase totals =	$881.20		$957.7720	$957.77	$957.70	$957.90