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	$244.78	13.452%	$277.7078	$277.71	$277.70	$277.70
Purchase #2	$112.78	12.128%	$126.458	$126.46	$126.45	$126.50
Purchase #3	$74.89	6.293%	$79.6028	$79.60	$79.60	$79.60
Purchase #4	$87.86	12.314%	$98.6791	$98.68	$98.70	$98.70
Purchase #5	$121.43	5.859%	$128.5446	$128.54	$128.55	$128.50
Purchase #6	$241.53	8.585%	$262.2654	$262.27	$262.25	$262.30
Purchase #7	$100.59	3.636%	$104.2475	$104.25	$104.25	$104.20
7 purchase totals =	$983.86		$1,077.5052	$1,077.51	$1,077.50	$1,077.50