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	$226.72	12.594%	$255.2731	$255.27	$255.25	$255.30
Purchase #2	$243.82	12.592%	$274.5218	$274.52	$274.50	$274.50
Purchase #3	$172.38	8.352%	$186.7772	$186.78	$186.80	$186.80
Purchase #4	$54.68	12.828%	$61.6944	$61.69	$61.70	$61.70
Purchase #5	$88.39	6.407%	$94.0531	$94.05	$94.05	$94.10
Purchase #6	$119.39	4.661%	$124.9548	$124.95	$124.95	$125.00
Purchase #7	$129.43	7.768%	$139.4841	$139.48	$139.50	$139.50
7 purchase totals =	$1,034.81		$1,136.7585	$1,136.74	$1,136.75	$1,136.90