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	$227.82	12.294%	$255.8282	$255.83	$255.85	$255.80
Purchase #2	$117.49	4.606%	$122.9016	$122.90	$122.90	$122.90
Purchase #3	$88.64	7.622%	$95.3961	$95.40	$95.40	$95.40
Purchase #4	$72.69	13.450%	$82.4668	$82.47	$82.45	$82.50
Purchase #5	$108.70	3.472%	$112.4741	$112.47	$112.45	$112.50
Purchase #6	$48.71	3.621%	$50.4738	$50.47	$50.45	$50.50
Purchase #7	$50.92	6.210%	$54.0821	$54.08	$54.10	$54.10
7 purchase totals =	$714.97		$773.6227	$773.62	$773.60	$773.70