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	$11.72	9.340%	$12.8146	$12.81	$12.80	$12.80
Purchase #2	$19.37	10.787%	$21.4594	$21.46	$21.45	$21.50
Purchase #3	$16.55	9.148%	$18.064	$18.06	$18.05	$18.10
Purchase #4	$199.97	13.767%	$227.4999	$227.50	$227.50	$227.50
Purchase #5	$232.77	3.848%	$241.727	$241.73	$241.75	$241.70
Purchase #6	$97.96	13.873%	$111.55	$111.55	$111.55	$111.60
Purchase #7	$11.60	12.827%	$13.0879	$13.09	$13.10	$13.10
7 purchase totals =	$589.94		$646.2028	$646.20	$646.20	$646.30