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	$143.72	13.723%	$163.4427	$163.44	$163.45	$163.40
Purchase #2	$87.93	3.129%	$90.6813	$90.68	$90.70	$90.70
Purchase #3	$52.39	3.551%	$54.2504	$54.25	$54.25	$54.30
Purchase #4	$142.69	9.184%	$155.7946	$155.79	$155.80	$155.80
Purchase #5	$43.37	12.516%	$48.7982	$48.80	$48.80	$48.80
Purchase #6	$103.64	12.716%	$116.8189	$116.82	$116.80	$116.80
Purchase #7	$143.26	11.348%	$159.5171	$159.52	$159.50	$159.50
7 purchase totals =	$717.00		$789.3032	$789.30	$789.30	$789.30