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	$172.89	4.301%	$180.326	$180.33	$180.35	$180.30
Purchase #2	$46.43	11.549%	$51.7922	$51.79	$51.80	$51.80
Purchase #3	$136.35	11.315%	$151.778	$151.78	$151.80	$151.80
Purchase #4	$70.60	11.333%	$78.6011	$78.60	$78.60	$78.60
Purchase #5	$49.48	12.388%	$55.6096	$55.61	$55.60	$55.60
Purchase #6	$119.81	8.398%	$129.8716	$129.87	$129.85	$129.90
Purchase #7	$30.91	10.340%	$34.1061	$34.11	$34.10	$34.10
7 purchase totals =	$626.47		$682.0846	$682.09	$682.10	$682.10