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	$9.79	12.626%	$11.0261	$11.03	$11.05	$11.00
Purchase #2	$52.40	4.717%	$54.8717	$54.87	$54.85	$54.90
Purchase #3	$8.81	3.268%	$9.0979	$9.10	$9.10	$9.10
Purchase #4	$171.27	6.733%	$182.8016	$182.80	$182.80	$182.80
Purchase #5	$85.66	4.485%	$89.5019	$89.50	$89.50	$89.50
Purchase #6	$68.46	5.354%	$72.1253	$72.13	$72.15	$72.10
Purchase #7	$83.82	8.153%	$90.6538	$90.65	$90.65	$90.70
7 purchase totals =	$480.21		$510.0783	$510.08	$510.10	$510.10