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	$30.28	7.609%	$32.584	$32.58	$32.60	$32.60
Purchase #2	$123.86	6.233%	$131.5802	$131.58	$131.60	$131.60
Purchase #3	$199.70	10.185%	$220.0394	$220.04	$220.05	$220.00
Purchase #4	$30.32	13.160%	$34.3101	$34.31	$34.30	$34.30
Purchase #5	$35.40	4.846%	$37.1155	$37.12	$37.10	$37.10
Purchase #6	$192.75	11.679%	$215.2613	$215.26	$215.25	$215.30
Purchase #7	$116.71	9.536%	$127.8395	$127.84	$127.85	$127.80
7 purchase totals =	$729.02		$798.7300	$798.73	$798.75	$798.70