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	$81.36	10.168%	$89.6327	$89.63	$89.65	$89.60
Purchase #2	$56.31	6.605%	$60.0293	$60.03	$60.05	$60.00
Purchase #3	$59.89	11.222%	$66.6109	$66.61	$66.60	$66.60
Purchase #4	$163.73	10.204%	$180.437	$180.44	$180.45	$180.40
Purchase #5	$104.47	11.734%	$116.7285	$116.73	$116.75	$116.70
Purchase #6	$78.72	3.696%	$81.6295	$81.63	$81.65	$81.60
Purchase #7	$194.56	9.189%	$212.4381	$212.44	$212.45	$212.40
7 purchase totals =	$739.04		$807.5060	$807.51	$807.60	$807.30