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	$235.32	3.865%	$244.4151	$244.42	$244.40	$244.40
Purchase #2	$250.66	8.150%	$271.0888	$271.09	$271.10	$271.10
Purchase #3	$17.71	10.238%	$19.5231	$19.52	$19.50	$19.50
Purchase #4	$104.72	6.808%	$111.8493	$111.85	$111.85	$111.80
Purchase #5	$117.82	13.176%	$133.344	$133.34	$133.35	$133.30
Purchase #6	$58.44	4.722%	$61.1995	$61.20	$61.20	$61.20
Purchase #7	$226.42	13.199%	$256.3052	$256.31	$256.30	$256.30
7 purchase totals =	$1,011.09		$1,097.7250	$1,097.73	$1,097.70	$1,097.60