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	$101.82	9.507%	$111.5	$111.50	$111.50	$111.50
Purchase #2	$70.32	11.395%	$78.333	$78.33	$78.35	$78.30
Purchase #3	$114.56	10.599%	$126.7022	$126.70	$126.70	$126.70
Purchase #4	$136.52	13.719%	$155.2492	$155.25	$155.25	$155.20
Purchase #5	$11.65	4.557%	$12.1809	$12.18	$12.20	$12.20
Purchase #6	$139.46	5.856%	$147.6268	$147.63	$147.65	$147.60
Purchase #7	$11.87	8.431%	$12.8708	$12.87	$12.85	$12.90
7 purchase totals =	$586.20		$644.4629	$644.46	$644.50	$644.40