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	$74.35	12.780%	$83.8519	$83.85	$83.85	$83.90
Purchase #2	$221.70	7.805%	$239.0037	$239.00	$239.00	$239.00
Purchase #3	$40.69	7.652%	$43.8036	$43.80	$43.80	$43.80
Purchase #4	$89.51	9.333%	$97.864	$97.86	$97.85	$97.90
Purchase #5	$114.66	11.540%	$127.8918	$127.89	$127.90	$127.90
Purchase #6	$204.87	10.128%	$225.6192	$225.62	$225.60	$225.60
Purchase #7	$11.93	4.476%	$12.464	$12.46	$12.45	$12.50
7 purchase totals =	$757.71		$830.4982	$830.48	$830.45	$830.60