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	$63.48	3.235%	$65.5336	$65.53	$65.55	$65.50
Purchase #2	$247.54	3.633%	$256.5331	$256.53	$256.55	$256.50
Purchase #3	$127.90	12.301%	$143.633	$143.63	$143.65	$143.60
Purchase #4	$142.72	5.700%	$150.855	$150.86	$150.85	$150.90
Purchase #5	$52.36	13.203%	$59.2731	$59.27	$59.25	$59.30
Purchase #6	$236.68	4.186%	$246.5874	$246.59	$246.60	$246.60
Purchase #7	$54.73	12.514%	$61.5789	$61.58	$61.60	$61.60
7 purchase totals =	$925.41		$983.9941	$983.99	$984.05	$984.00