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	$29.70	10.780%	$32.9017	$32.90	$32.90	$32.90
Purchase #2	$131.60	9.159%	$143.6532	$143.65	$143.65	$143.70
Purchase #3	$178.52	5.491%	$188.3225	$188.32	$188.30	$188.30
Purchase #4	$73.30	6.217%	$77.8571	$77.86	$77.85	$77.90
Purchase #5	$26.83	8.758%	$29.1798	$29.18	$29.20	$29.20
Purchase #6	$233.28	9.710%	$255.9315	$255.93	$255.95	$255.90
Purchase #7	$112.68	10.557%	$124.5756	$124.58	$124.60	$124.60
7 purchase totals =	$785.91		$852.4214	$852.42	$852.45	$852.50