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	$8.58	11.388%	$9.5571	$9.56	$9.55	$9.60
Purchase #2	$111.86	6.261%	$118.8636	$118.86	$118.85	$118.90
Purchase #3	$210.42	9.769%	$230.9759	$230.98	$231.00	$231.00
Purchase #4	$172.84	4.806%	$181.1467	$181.15	$181.15	$181.10
Purchase #5	$78.89	13.367%	$89.4352	$89.44	$89.45	$89.40
Purchase #6	$165.46	6.742%	$176.6153	$176.62	$176.60	$176.60
Purchase #7	$179.71	11.432%	$200.2544	$200.25	$200.25	$200.30
7 purchase totals =	$927.76		$1,006.8482	$1,006.86	$1,006.85	$1,006.90