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	$13.50	6.422%	$14.367	$14.37	$14.35	$14.40
Purchase #2	$126.35	10.536%	$139.6622	$139.66	$139.65	$139.70
Purchase #3	$73.94	5.602%	$78.0821	$78.08	$78.10	$78.10
Purchase #4	$171.57	8.238%	$185.7039	$185.70	$185.70	$185.70
Purchase #5	$32.90	4.323%	$34.3223	$34.32	$34.30	$34.30
Purchase #6	$129.42	7.409%	$139.0087	$139.01	$139.00	$139.00
Purchase #7	$29.35	9.424%	$32.1159	$32.12	$32.10	$32.10
7 purchase totals =	$577.03		$623.2621	$623.26	$623.20	$623.30