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	$234.98	8.784%	$255.6206	$255.62	$255.60	$255.60
Purchase #2	$151.52	3.246%	$156.4383	$156.44	$156.45	$156.40
Purchase #3	$45.54	9.133%	$49.6992	$49.70	$49.70	$49.70
Purchase #4	$34.46	13.631%	$39.1572	$39.16	$39.15	$39.20
Purchase #5	$118.96	11.262%	$132.3573	$132.36	$132.35	$132.40
Purchase #6	$193.72	3.614%	$200.721	$200.72	$200.70	$200.70
Purchase #7	$75.75	12.783%	$85.4331	$85.43	$85.45	$85.40
7 purchase totals =	$854.93		$919.4267	$919.43	$919.40	$919.40