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	$250.56	3.287%	$258.7959	$258.80	$258.80	$258.80
Purchase #2	$230.83	10.783%	$255.7204	$255.72	$255.70	$255.70
Purchase #3	$119.60	6.226%	$127.0463	$127.05	$127.05	$127.00
Purchase #4	$131.51	11.203%	$146.2431	$146.24	$146.25	$146.20
Purchase #5	$83.82	3.186%	$86.4905	$86.49	$86.50	$86.50
Purchase #6	$19.84	3.845%	$20.6028	$20.60	$20.60	$20.60
Purchase #7	$72.88	3.439%	$75.3863	$75.39	$75.40	$75.40
7 purchase totals =	$909.04		$970.2853	$970.29	$970.30	$970.20