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	$197.35	6.712%	$210.5961	$210.60	$210.60	$210.60
Purchase #2	$96.74	3.322%	$99.9537	$99.95	$99.95	$100.00
Purchase #3	$124.47	9.714%	$136.561	$136.56	$136.55	$136.60
Purchase #4	$199.89	8.751%	$217.3824	$217.38	$217.40	$217.40
Purchase #5	$107.45	10.265%	$118.4797	$118.48	$118.50	$118.50
Purchase #6	$163.85	4.127%	$170.6121	$170.61	$170.60	$170.60
Purchase #7	$103.75	13.259%	$117.5062	$117.51	$117.50	$117.50
7 purchase totals =	$993.50		$1,071.0912	$1,071.09	$1,071.10	$1,071.20