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	$233.95	5.620%	$247.098	$247.10	$247.10	$247.10
Purchase #2	$50.66	7.362%	$54.3896	$54.39	$54.40	$54.40
Purchase #3	$97.30	6.237%	$103.3686	$103.37	$103.35	$103.40
Purchase #4	$118.45	6.635%	$126.3092	$126.31	$126.30	$126.30
Purchase #5	$59.54	4.227%	$62.0568	$62.06	$62.05	$62.10
Purchase #6	$206.52	13.438%	$234.2722	$234.27	$234.25	$234.30
Purchase #7	$58.83	6.110%	$62.4245	$62.42	$62.40	$62.40
7 purchase totals =	$825.25		$889.9189	$889.92	$889.85	$890.00