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	$62.36	6.869%	$66.6435	$66.64	$66.65	$66.60
Purchase #2	$236.67	10.845%	$262.3369	$262.34	$262.35	$262.30
Purchase #3	$55.88	10.645%	$61.8284	$61.83	$61.85	$61.80
Purchase #4	$79.62	13.567%	$90.422	$90.42	$90.40	$90.40
Purchase #5	$124.32	11.724%	$138.8953	$138.90	$138.90	$138.90
Purchase #6	$228.70	12.646%	$257.6214	$257.62	$257.60	$257.60
Purchase #7	$243.78	12.713%	$274.7718	$274.77	$274.75	$274.80
7 purchase totals =	$1,031.33		$1,152.5193	$1,152.52	$1,152.50	$1,152.40