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	$132.37	8.845%	$144.0781	$144.08	$144.10	$144.10
Purchase #2	$193.36	12.305%	$217.1529	$217.15	$217.15	$217.20
Purchase #3	$30.75	4.217%	$32.0467	$32.05	$32.05	$32.00
Purchase #4	$36.98	6.830%	$39.5057	$39.51	$39.50	$39.50
Purchase #5	$129.83	9.256%	$141.8471	$141.85	$141.85	$141.80
Purchase #6	$54.77	9.191%	$59.8039	$59.80	$59.80	$59.80
Purchase #7	$149.75	12.333%	$168.2187	$168.22	$168.20	$168.20
7 purchase totals =	$727.81		$802.6531	$802.66	$802.65	$802.60