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	$242.73	5.636%	$256.4103	$256.41	$256.40	$256.40
Purchase #2	$113.51	8.647%	$123.3252	$123.33	$123.35	$123.30
Purchase #3	$60.89	4.715%	$63.761	$63.76	$63.75	$63.80
Purchase #4	$207.87	10.724%	$230.162	$230.16	$230.15	$230.20
Purchase #5	$246.65	3.493%	$255.2655	$255.27	$255.25	$255.30
Purchase #6	$69.44	10.460%	$76.7034	$76.70	$76.70	$76.70
Purchase #7	$29.30	13.650%	$33.2995	$33.30	$33.30	$33.30
7 purchase totals =	$970.39		$1,038.9269	$1,038.93	$1,038.90	$1,039.00