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	$231.97	10.347%	$255.9719	$255.97	$255.95	$256.00
Purchase #2	$168.54	11.347%	$187.6642	$187.66	$187.65	$187.70
Purchase #3	$62.60	5.548%	$66.073	$66.07	$66.05	$66.10
Purchase #4	$54.46	13.529%	$61.8279	$61.83	$61.85	$61.80
Purchase #5	$52.54	4.606%	$54.96	$54.96	$54.95	$55.00
Purchase #6	$5.71	7.556%	$6.1414	$6.14	$6.15	$6.10
Purchase #7	$79.28	12.358%	$89.0774	$89.08	$89.10	$89.10
7 purchase totals =	$655.10		$721.7158	$721.71	$721.70	$721.80