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	$132.65	3.857%	$137.7663	$137.77	$137.75	$137.80
Purchase #2	$84.77	6.850%	$90.5767	$90.58	$90.60	$90.60
Purchase #3	$176.90	13.190%	$200.2331	$200.23	$200.25	$200.20
Purchase #4	$48.57	11.301%	$54.0589	$54.06	$54.05	$54.10
Purchase #5	$94.72	7.286%	$101.6213	$101.62	$101.60	$101.60
Purchase #6	$41.73	6.504%	$44.4441	$44.44	$44.45	$44.40
Purchase #7	$52.81	8.425%	$57.2592	$57.26	$57.25	$57.30
7 purchase totals =	$632.15		$685.9596	$685.96	$685.95	$686.00