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	$56.72	4.762%	$59.421	$59.42	$59.40	$59.40
Purchase #2	$154.86	4.344%	$161.5871	$161.59	$161.60	$161.60
Purchase #3	$149.82	6.735%	$159.9104	$159.91	$159.90	$159.90
Purchase #4	$236.45	12.266%	$265.453	$265.45	$265.45	$265.50
Purchase #5	$48.59	11.289%	$54.0753	$54.08	$54.10	$54.10
Purchase #6	$224.89	3.698%	$233.2064	$233.21	$233.20	$233.20
Purchase #7	$62.77	5.113%	$65.9794	$65.98	$66.00	$66.00
7 purchase totals =	$934.10		$999.6326	$999.64	$999.65	$999.70