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	$61.54	8.224%	$66.601	$66.60	$66.60	$66.60
Purchase #2	$198.87	8.415%	$215.6049	$215.60	$215.60	$215.60
Purchase #3	$37.25	4.780%	$39.0306	$39.03	$39.05	$39.00
Purchase #4	$237.78	4.627%	$248.7821	$248.78	$248.80	$248.80
Purchase #5	$145.89	8.794%	$158.7196	$158.72	$158.70	$158.70
Purchase #6	$127.55	12.839%	$143.9261	$143.93	$143.95	$143.90
Purchase #7	$83.47	7.811%	$89.9898	$89.99	$90.00	$90.00
7 purchase totals =	$892.35		$962.6541	$962.65	$962.70	$962.60