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	$250.39	8.397%	$271.4152	$271.42	$271.40	$271.40
Purchase #2	$152.62	12.373%	$171.5037	$171.50	$171.50	$171.50
Purchase #3	$40.85	12.780%	$46.0706	$46.07	$46.05	$46.10
Purchase #4	$117.39	4.595%	$122.7841	$122.78	$122.80	$122.80
Purchase #5	$8.79	13.504%	$9.977	$9.98	$10.00	$10.00
Purchase #6	$118.50	4.436%	$123.7567	$123.76	$123.75	$123.80
Purchase #7	$97.83	13.750%	$111.2816	$111.28	$111.30	$111.30
7 purchase totals =	$786.37		$856.7889	$856.79	$856.80	$856.90