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	$138.52	4.153%	$144.2727	$144.27	$144.25	$144.30
Purchase #2	$109.88	10.600%	$121.5273	$121.53	$121.55	$121.50
Purchase #3	$208.68	9.772%	$229.0722	$229.07	$229.05	$229.10
Purchase #4	$217.82	5.365%	$229.506	$229.51	$229.50	$229.50
Purchase #5	$96.71	6.626%	$103.118	$103.12	$103.10	$103.10
Purchase #6	$82.68	8.691%	$89.8657	$89.87	$89.85	$89.90
Purchase #7	$164.31	8.130%	$177.6684	$177.67	$177.65	$177.70
7 purchase totals =	$1,018.60		$1,095.0303	$1,095.04	$1,094.95	$1,095.10