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	$51.51	8.381%	$55.8271	$55.83	$55.85	$55.80
Purchase #2	$129.70	11.498%	$144.6129	$144.61	$144.60	$144.60
Purchase #3	$245.58	3.368%	$253.8511	$253.85	$253.85	$253.90
Purchase #4	$126.54	13.393%	$143.4875	$143.49	$143.50	$143.50
Purchase #5	$241.57	10.748%	$267.5339	$267.53	$267.55	$267.50
Purchase #6	$194.83	3.505%	$201.6588	$201.66	$201.65	$201.70
Purchase #7	$29.51	11.448%	$32.8883	$32.89	$32.90	$32.90
7 purchase totals =	$1,019.24		$1,099.8596	$1,099.86	$1,099.90	$1,099.90