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	$14.75	7.766%	$15.8955	$15.90	$15.90	$15.90
Purchase #2	$123.90	13.575%	$140.7194	$140.72	$140.70	$140.70
Purchase #3	$29.82	5.622%	$31.4965	$31.50	$31.50	$31.50
Purchase #4	$123.42	10.580%	$136.4778	$136.48	$136.50	$136.50
Purchase #5	$77.93	7.665%	$83.9033	$83.90	$83.90	$83.90
Purchase #6	$61.74	13.203%	$69.8915	$69.89	$69.90	$69.90
Purchase #7	$85.89	10.274%	$94.7143	$94.71	$94.70	$94.70
7 purchase totals =	$517.45		$573.0983	$573.10	$573.10	$573.10