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	$226.33	3.598%	$234.4734	$234.47	$234.45	$234.50
Purchase #2	$200.50	11.656%	$223.8703	$223.87	$223.85	$223.90
Purchase #3	$96.67	11.733%	$108.0123	$108.01	$108.00	$108.00
Purchase #4	$33.58	13.151%	$37.9961	$38.00	$38.00	$38.00
Purchase #5	$11.52	5.340%	$12.1352	$12.14	$12.15	$12.10
Purchase #6	$197.42	12.246%	$221.5961	$221.60	$221.60	$221.60
Purchase #7	$82.32	10.381%	$90.8656	$90.87	$90.85	$90.90
7 purchase totals =	$848.34		$928.9490	$928.96	$928.90	$929.00