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	$45.84	9.457%	$50.1751	$50.18	$50.20	$50.20
Purchase #2	$128.55	9.719%	$141.0438	$141.04	$141.05	$141.00
Purchase #3	$50.77	6.561%	$54.101	$54.10	$54.10	$54.10
Purchase #4	$235.53	8.874%	$256.4309	$256.43	$256.45	$256.40
Purchase #5	$19.82	7.230%	$21.253	$21.25	$21.25	$21.30
Purchase #6	$96.43	9.569%	$105.6574	$105.66	$105.65	$105.70
Purchase #7	$13.96	13.841%	$15.8922	$15.89	$15.90	$15.90
7 purchase totals =	$590.90		$644.5534	$644.55	$644.60	$644.60