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	$95.79	11.397%	$106.7072	$106.71	$106.70	$106.70
Purchase #2	$41.83	5.734%	$44.2285	$44.23	$44.25	$44.20
Purchase #3	$162.57	13.509%	$184.5316	$184.53	$184.55	$184.50
Purchase #4	$38.26	6.863%	$40.8858	$40.89	$40.90	$40.90
Purchase #5	$103.70	13.591%	$117.7939	$117.79	$117.80	$117.80
Purchase #6	$99.73	5.172%	$104.888	$104.89	$104.90	$104.90
Purchase #7	$10.89	13.692%	$12.3811	$12.38	$12.40	$12.40
7 purchase totals =	$552.77		$611.4161	$611.42	$611.50	$611.40