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	$24.87	9.858%	$27.3217	$27.32	$27.30	$27.30
Purchase #2	$134.98	6.597%	$143.8846	$143.88	$143.90	$143.90
Purchase #3	$233.50	4.626%	$244.3017	$244.30	$244.30	$244.30
Purchase #4	$241.52	6.246%	$256.6053	$256.61	$256.60	$256.60
Purchase #5	$139.63	3.676%	$144.7628	$144.76	$144.75	$144.80
Purchase #6	$64.49	9.656%	$70.7172	$70.72	$70.70	$70.70
Purchase #7	$104.48	11.713%	$116.7177	$116.72	$116.70	$116.70
7 purchase totals =	$943.47		$1,004.3110	$1,004.31	$1,004.25	$1,004.30