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	$131.78	3.607%	$136.5333	$136.53	$136.55	$136.50
Purchase #2	$47.94	13.550%	$54.4359	$54.44	$54.45	$54.40
Purchase #3	$58.47	5.209%	$61.5157	$61.52	$61.50	$61.50
Purchase #4	$80.45	8.344%	$87.1627	$87.16	$87.15	$87.20
Purchase #5	$57.95	5.874%	$61.354	$61.35	$61.35	$61.40
Purchase #6	$63.57	6.336%	$67.5978	$67.60	$67.60	$67.60
Purchase #7	$92.89	12.605%	$104.5988	$104.60	$104.60	$104.60
7 purchase totals =	$533.05		$573.1982	$573.20	$573.20	$573.20