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	$63.67	10.660%	$70.4572	$70.46	$70.45	$70.50
Purchase #2	$79.78	10.255%	$87.9614	$87.96	$87.95	$88.00
Purchase #3	$98.56	13.456%	$111.8222	$111.82	$111.80	$111.80
Purchase #4	$217.99	6.724%	$232.6476	$232.65	$232.65	$232.60
Purchase #5	$222.78	11.719%	$248.8876	$248.89	$248.90	$248.90
Purchase #6	$39.87	4.161%	$41.529	$41.53	$41.55	$41.50
Purchase #7	$33.91	9.500%	$37.1315	$37.13	$37.15	$37.10
7 purchase totals =	$756.56		$830.4365	$830.44	$830.45	$830.40