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	$159.28	12.309%	$178.8858	$178.89	$178.90	$178.90
Purchase #2	$153.72	9.381%	$168.1405	$168.14	$168.15	$168.10
Purchase #3	$150.71	5.342%	$158.7609	$158.76	$158.75	$158.80
Purchase #4	$44.84	3.574%	$46.4426	$46.44	$46.45	$46.40
Purchase #5	$13.80	7.483%	$14.8327	$14.83	$14.85	$14.80
Purchase #6	$230.75	11.593%	$257.5008	$257.50	$257.50	$257.50
Purchase #7	$40.31	13.332%	$45.6841	$45.68	$45.70	$45.70
7 purchase totals =	$793.41		$870.2474	$870.24	$870.30	$870.20