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	$46.60	9.847%	$51.1887	$51.19	$51.20	$51.20
Purchase #2	$139.71	3.119%	$144.0676	$144.07	$144.05	$144.10
Purchase #3	$112.61	12.520%	$126.7088	$126.71	$126.70	$126.70
Purchase #4	$12.52	3.491%	$12.9571	$12.96	$12.95	$13.00
Purchase #5	$55.29	8.110%	$59.774	$59.77	$59.75	$59.80
Purchase #6	$18.89	10.234%	$20.8232	$20.82	$20.80	$20.80
Purchase #7	$240.85	3.148%	$248.432	$248.43	$248.45	$248.40
7 purchase totals =	$626.47		$663.9514	$663.95	$663.90	$664.00