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	$11.73	5.424%	$12.3662	$12.37	$12.35	$12.40
Purchase #2	$248.66	11.244%	$276.6193	$276.62	$276.60	$276.60
Purchase #3	$25.53	9.248%	$27.891	$27.89	$27.90	$27.90
Purchase #4	$52.54	4.313%	$54.8061	$54.81	$54.80	$54.80
Purchase #5	$173.53	4.184%	$180.7905	$180.79	$180.80	$180.80
Purchase #6	$20.32	3.426%	$21.0162	$21.02	$21.00	$21.00
Purchase #7	$49.72	6.696%	$53.0493	$53.05	$53.05	$53.00
7 purchase totals =	$582.03		$626.5386	$626.55	$626.50	$626.50