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	$26.54	11.186%	$29.5088	$29.51	$29.50	$29.50
Purchase #2	$111.60	11.257%	$124.1628	$124.16	$124.15	$124.20
Purchase #3	$12.46	8.435%	$13.511	$13.51	$13.50	$13.50
Purchase #4	$44.99	5.724%	$47.5652	$47.57	$47.55	$47.60
Purchase #5	$55.59	11.272%	$61.8561	$61.86	$61.85	$61.90
Purchase #6	$78.38	3.384%	$81.0324	$81.03	$81.05	$81.00
Purchase #7	$116.48	5.829%	$123.2696	$123.27	$123.25	$123.30
7 purchase totals =	$446.04		$480.9059	$480.91	$480.85	$481.00