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	$99.59	6.654%	$106.2167	$106.22	$106.20	$106.20
Purchase #2	$23.70	13.252%	$26.8407	$26.84	$26.85	$26.80
Purchase #3	$78.40	5.146%	$82.4345	$82.43	$82.45	$82.40
Purchase #4	$76.31	8.652%	$82.9123	$82.91	$82.90	$82.90
Purchase #5	$63.60	4.738%	$66.6134	$66.61	$66.60	$66.60
Purchase #6	$60.47	11.472%	$67.4071	$67.41	$67.40	$67.40
Purchase #7	$70.75	9.802%	$77.6849	$77.68	$77.70	$77.70
7 purchase totals =	$472.82		$510.1096	$510.10	$510.10	$510.00