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	$20.89	8.204%	$22.6038	$22.60	$22.60	$22.60
Purchase #2	$52.63	3.116%	$54.27	$54.27	$54.25	$54.30
Purchase #3	$127.95	9.849%	$140.5518	$140.55	$140.55	$140.60
Purchase #4	$85.49	6.313%	$90.887	$90.89	$90.90	$90.90
Purchase #5	$76.29	5.565%	$80.5355	$80.54	$80.55	$80.50
Purchase #6	$141.55	13.737%	$160.9947	$160.99	$161.00	$161.00
Purchase #7	$183.61	13.730%	$208.8197	$208.82	$208.80	$208.80
7 purchase totals =	$688.41		$758.6625	$758.66	$758.65	$758.70