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	$56.84	5.291%	$59.8474	$59.85	$59.85	$59.80
Purchase #2	$116.89	10.313%	$128.9449	$128.94	$128.95	$128.90
Purchase #3	$237.65	13.775%	$270.3863	$270.39	$270.40	$270.40
Purchase #4	$70.27	11.828%	$78.5815	$78.58	$78.60	$78.60
Purchase #5	$227.27	3.243%	$234.6404	$234.64	$234.65	$234.60
Purchase #6	$241.95	12.208%	$271.4873	$271.49	$271.50	$271.50
Purchase #7	$180.86	13.456%	$205.1965	$205.20	$205.20	$205.20
7 purchase totals =	$1,131.73		$1,249.0843	$1,249.09	$1,249.15	$1,249.00