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	$48.45	12.680%	$54.5935	$54.59	$54.60	$54.60
Purchase #2	$208.62	11.599%	$232.8178	$232.82	$232.80	$232.80
Purchase #3	$132.89	13.652%	$151.0321	$151.03	$151.05	$151.00
Purchase #4	$52.53	6.193%	$55.7832	$55.78	$55.80	$55.80
Purchase #5	$141.90	4.294%	$147.9932	$147.99	$148.00	$148.00
Purchase #6	$98.84	12.839%	$111.5301	$111.53	$111.55	$111.50
Purchase #7	$176.81	5.498%	$186.531	$186.53	$186.55	$186.50
7 purchase totals =	$860.04		$940.2809	$940.27	$940.35	$940.20