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	$233.62	11.189%	$259.7597	$259.76	$259.75	$259.80
Purchase #2	$82.55	3.515%	$85.4516	$85.45	$85.45	$85.50
Purchase #3	$63.60	12.828%	$71.7586	$71.76	$71.75	$71.80
Purchase #4	$206.51	13.688%	$234.7771	$234.78	$234.80	$234.80
Purchase #5	$247.39	7.201%	$265.2046	$265.20	$265.20	$265.20
Purchase #6	$138.47	3.837%	$143.7831	$143.78	$143.80	$143.80
Purchase #7	$37.45	3.793%	$38.8705	$38.87	$38.85	$38.90
7 purchase totals =	$1,009.59		$1,099.6052	$1,099.60	$1,099.60	$1,099.80