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	$237.41	4.681%	$248.5232	$248.52	$248.50	$248.50
Purchase #2	$48.77	3.276%	$50.3677	$50.37	$50.35	$50.40
Purchase #3	$241.63	11.168%	$268.6152	$268.62	$268.60	$268.60
Purchase #4	$32.45	7.310%	$34.8221	$34.82	$34.80	$34.80
Purchase #5	$97.99	13.707%	$111.4215	$111.42	$111.40	$111.40
Purchase #6	$46.76	3.494%	$48.3938	$48.39	$48.40	$48.40
Purchase #7	$42.82	4.648%	$44.8103	$44.81	$44.80	$44.80
7 purchase totals =	$747.83		$806.9538	$806.95	$806.85	$806.90