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	$37.96	6.523%	$40.4361	$40.44	$40.45	$40.40
Purchase #2	$243.70	8.844%	$265.2528	$265.25	$265.25	$265.30
Purchase #3	$126.42	5.694%	$133.6184	$133.62	$133.60	$133.60
Purchase #4	$18.37	6.253%	$19.5187	$19.52	$19.50	$19.50
Purchase #5	$85.66	3.189%	$88.3917	$88.39	$88.40	$88.40
Purchase #6	$231.79	10.204%	$255.4419	$255.44	$255.45	$255.40
Purchase #7	$48.72	10.491%	$53.8312	$53.83	$53.85	$53.80
7 purchase totals =	$792.62		$856.4908	$856.49	$856.50	$856.40