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	$57.51	9.720%	$63.1	$63.10	$63.10	$63.10
Purchase #2	$42.62	11.664%	$47.5912	$47.59	$47.60	$47.60
Purchase #3	$100.85	10.581%	$111.5209	$111.52	$111.50	$111.50
Purchase #4	$131.28	5.118%	$137.9989	$138.00	$138.00	$138.00
Purchase #5	$50.25	8.427%	$54.4846	$54.48	$54.50	$54.50
Purchase #6	$69.57	11.775%	$77.7619	$77.76	$77.75	$77.80
Purchase #7	$154.57	11.519%	$172.3749	$172.37	$172.35	$172.40
7 purchase totals =	$606.65		$664.8324	$664.82	$664.80	$664.90