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	$78.92	11.209%	$87.7661	$87.77	$87.75	$87.80
Purchase #2	$106.65	9.323%	$116.593	$116.59	$116.60	$116.60
Purchase #3	$134.72	10.259%	$148.5409	$148.54	$148.55	$148.50
Purchase #4	$109.94	7.820%	$118.5373	$118.54	$118.55	$118.50
Purchase #5	$127.69	13.307%	$144.6817	$144.68	$144.70	$144.70
Purchase #6	$241.60	11.583%	$269.5845	$269.58	$269.60	$269.60
Purchase #7	$72.91	8.447%	$79.0687	$79.07	$79.05	$79.10
7 purchase totals =	$872.43		$964.7722	$964.77	$964.80	$964.80