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	$229.27	11.396%	$255.3976	$255.40	$255.40	$255.40
Purchase #2	$35.77	10.693%	$39.5949	$39.59	$39.60	$39.60
Purchase #3	$37.41	5.435%	$39.4432	$39.44	$39.45	$39.40
Purchase #4	$50.88	6.189%	$54.029	$54.03	$54.05	$54.00
Purchase #5	$239.99	5.781%	$253.8638	$253.86	$253.85	$253.90
Purchase #6	$61.90	12.868%	$69.8653	$69.87	$69.85	$69.90
Purchase #7	$178.70	6.520%	$190.3512	$190.35	$190.35	$190.40
7 purchase totals =	$833.92		$902.5450	$902.54	$902.55	$902.60