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	$156.81	13.813%	$178.4702	$178.47	$178.45	$178.50
Purchase #2	$100.38	10.632%	$111.0524	$111.05	$111.05	$111.10
Purchase #3	$51.98	10.797%	$57.5923	$57.59	$57.60	$57.60
Purchase #4	$34.90	12.450%	$39.2451	$39.25	$39.25	$39.20
Purchase #5	$122.49	12.526%	$137.8331	$137.83	$137.85	$137.80
Purchase #6	$5.94	7.317%	$6.3746	$6.37	$6.35	$6.40
Purchase #7	$38.86	4.693%	$40.6837	$40.68	$40.70	$40.70
7 purchase totals =	$511.36		$571.2514	$571.24	$571.25	$571.30