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	$76.61	6.408%	$81.5192	$81.52	$81.50	$81.50
Purchase #2	$84.86	11.652%	$94.7479	$94.75	$94.75	$94.70
Purchase #3	$210.69	5.725%	$222.752	$222.75	$222.75	$222.80
Purchase #4	$99.39	13.542%	$112.8494	$112.85	$112.85	$112.80
Purchase #5	$72.86	5.588%	$76.9314	$76.93	$76.95	$76.90
Purchase #6	$31.40	11.277%	$34.941	$34.94	$34.95	$34.90
Purchase #7	$40.31	3.815%	$41.8478	$41.85	$41.85	$41.80
7 purchase totals =	$616.12		$665.5887	$665.59	$665.60	$665.40