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	$39.67	3.528%	$41.0696	$41.07	$41.05	$41.10
Purchase #2	$37.57	8.678%	$40.8303	$40.83	$40.85	$40.80
Purchase #3	$34.64	9.234%	$37.8387	$37.84	$37.85	$37.80
Purchase #4	$210.72	3.120%	$217.2945	$217.29	$217.30	$217.30
Purchase #5	$10.41	9.561%	$11.4053	$11.41	$11.40	$11.40
Purchase #6	$61.31	11.360%	$68.2748	$68.27	$68.25	$68.30
Purchase #7	$9.91	3.273%	$10.2344	$10.23	$10.25	$10.20
7 purchase totals =	$404.23		$426.9476	$426.94	$426.95	$426.90