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	$82.81	8.271%	$89.6592	$89.66	$89.65	$89.70
Purchase #2	$161.53	6.178%	$171.5093	$171.51	$171.50	$171.50
Purchase #3	$33.82	5.857%	$35.8008	$35.80	$35.80	$35.80
Purchase #4	$76.53	3.172%	$78.9575	$78.96	$78.95	$79.00
Purchase #5	$48.94	4.466%	$51.1257	$51.13	$51.15	$51.10
Purchase #6	$10.46	5.487%	$11.0339	$11.03	$11.05	$11.00
Purchase #7	$223.77	4.561%	$233.9761	$233.98	$234.00	$234.00
7 purchase totals =	$637.86		$672.0625	$672.07	$672.10	$672.10