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	$115.96	11.239%	$128.9927	$128.99	$129.00	$129.00
Purchase #2	$141.42	10.233%	$155.8915	$155.89	$155.90	$155.90
Purchase #3	$59.52	3.576%	$61.6484	$61.65	$61.65	$61.60
Purchase #4	$19.89	9.626%	$21.8046	$21.80	$21.80	$21.80
Purchase #5	$147.72	7.735%	$159.1461	$159.15	$159.15	$159.10
Purchase #6	$100.71	7.784%	$108.5493	$108.55	$108.55	$108.50
Purchase #7	$236.31	4.352%	$246.5942	$246.59	$246.60	$246.60
7 purchase totals =	$821.53		$882.6268	$882.62	$882.65	$882.50