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	$30.98	4.187%	$32.2771	$32.28	$32.30	$32.30
Purchase #2	$69.64	10.434%	$76.9062	$76.91	$76.90	$76.90
Purchase #3	$60.52	10.406%	$66.8177	$66.82	$66.80	$66.80
Purchase #4	$44.60	5.302%	$46.9647	$46.96	$46.95	$47.00
Purchase #5	$25.33	3.254%	$26.1542	$26.15	$26.15	$26.20
Purchase #6	$80.55	12.300%	$90.4577	$90.46	$90.45	$90.50
Purchase #7	$151.80	9.224%	$165.802	$165.80	$165.80	$165.80
7 purchase totals =	$463.42		$505.3796	$505.38	$505.35	$505.50