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	$129.73	11.383%	$144.4972	$144.50	$144.50	$144.50
Purchase #2	$33.47	4.195%	$34.8741	$34.87	$34.85	$34.90
Purchase #3	$111.87	8.862%	$121.7839	$121.78	$121.80	$121.80
Purchase #4	$75.87	13.806%	$86.3446	$86.34	$86.35	$86.30
Purchase #5	$28.34	13.838%	$32.2617	$32.26	$32.25	$32.30
Purchase #6	$171.50	10.648%	$189.7613	$189.76	$189.75	$189.80
Purchase #7	$49.83	7.268%	$53.4516	$53.45	$53.45	$53.50
7 purchase totals =	$600.61		$662.9744	$662.96	$662.95	$663.10