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	$244.43	4.719%	$255.9647	$255.96	$255.95	$256.00
Purchase #2	$249.73	8.644%	$271.3167	$271.32	$271.30	$271.30
Purchase #3	$228.52	12.413%	$256.8862	$256.89	$256.90	$256.90
Purchase #4	$104.57	8.541%	$113.5013	$113.50	$113.50	$113.50
Purchase #5	$102.83	13.123%	$116.3244	$116.32	$116.30	$116.30
Purchase #6	$19.61	9.213%	$21.4167	$21.42	$21.40	$21.40
Purchase #7	$145.58	5.510%	$153.6015	$153.60	$153.60	$153.60
7 purchase totals =	$1,095.27		$1,189.0115	$1,189.01	$1,188.95	$1,189.00