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	$112.92	13.475%	$128.136	$128.14	$128.15	$128.10
Purchase #2	$108.48	7.388%	$116.4945	$116.49	$116.50	$116.50
Purchase #3	$177.91	11.856%	$199.003	$199.00	$199.00	$199.00
Purchase #4	$231.90	12.397%	$260.6486	$260.65	$260.65	$260.60
Purchase #5	$94.42	13.245%	$106.9259	$106.93	$106.95	$106.90
Purchase #6	$100.64	11.516%	$112.2297	$112.23	$112.25	$112.20
Purchase #7	$51.27	5.525%	$54.1027	$54.10	$54.10	$54.10
7 purchase totals =	$877.54		$977.5404	$977.54	$977.60	$977.40