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	$78.80	3.614%	$81.6478	$81.65	$81.65	$81.60
Purchase #2	$141.65	9.696%	$155.3844	$155.38	$155.40	$155.40
Purchase #3	$89.33	12.591%	$100.5775	$100.58	$100.60	$100.60
Purchase #4	$225.88	12.126%	$253.2702	$253.27	$253.25	$253.30
Purchase #5	$121.57	8.554%	$131.9691	$131.97	$131.95	$132.00
Purchase #6	$221.63	13.287%	$251.078	$251.08	$251.10	$251.10
Purchase #7	$112.59	11.825%	$125.9038	$125.90	$125.90	$125.90
7 purchase totals =	$991.45		$1,099.8308	$1,099.83	$1,099.85	$1,099.90