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	$248.89	9.516%	$272.5744	$272.57	$272.55	$272.60
Purchase #2	$13.83	6.726%	$14.7602	$14.76	$14.75	$14.80
Purchase #3	$205.31	11.396%	$228.7071	$228.71	$228.70	$228.70
Purchase #4	$103.72	12.164%	$116.3365	$116.34	$116.35	$116.30
Purchase #5	$179.73	5.171%	$189.0238	$189.02	$189.00	$189.00
Purchase #6	$89.66	5.528%	$94.6164	$94.62	$94.60	$94.60
Purchase #7	$37.79	6.559%	$40.2686	$40.27	$40.25	$40.30
7 purchase totals =	$878.93		$956.2870	$956.29	$956.20	$956.30