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	$108.38	13.841%	$123.3809	$123.38	$123.40	$123.40
Purchase #2	$75.51	13.797%	$85.9281	$85.93	$85.95	$85.90
Purchase #3	$83.95	7.839%	$90.5308	$90.53	$90.55	$90.50
Purchase #4	$240.52	5.363%	$253.4191	$253.42	$253.40	$253.40
Purchase #5	$204.28	7.716%	$220.0422	$220.04	$220.05	$220.00
Purchase #6	$35.87	8.227%	$38.821	$38.82	$38.80	$38.80
Purchase #7	$143.76	10.387%	$158.6924	$158.69	$158.70	$158.70
7 purchase totals =	$892.27		$970.8145	$970.81	$970.85	$970.70