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	$50.94	7.115%	$54.5644	$54.56	$54.55	$54.60
Purchase #2	$49.96	11.840%	$55.8753	$55.88	$55.90	$55.90
Purchase #3	$136.66	4.549%	$142.8767	$142.88	$142.90	$142.90
Purchase #4	$50.83	9.348%	$55.5816	$55.58	$55.60	$55.60
Purchase #5	$131.96	10.688%	$146.0639	$146.06	$146.05	$146.10
Purchase #6	$239.92	5.519%	$253.1612	$253.16	$253.15	$253.20
Purchase #7	$26.86	13.283%	$30.4278	$30.43	$30.45	$30.40
7 purchase totals =	$687.13		$738.5509	$738.55	$738.60	$738.70