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	$241.87	3.153%	$249.4962	$249.50	$249.50	$249.50
Purchase #2	$128.35	12.443%	$144.3206	$144.32	$144.30	$144.30
Purchase #3	$104.89	6.757%	$111.9774	$111.98	$112.00	$112.00
Purchase #4	$77.86	11.353%	$86.6994	$86.70	$86.70	$86.70
Purchase #5	$51.98	13.639%	$59.0696	$59.07	$59.05	$59.10
Purchase #6	$28.46	12.580%	$32.0403	$32.04	$32.05	$32.00
Purchase #7	$33.40	4.725%	$34.9782	$34.98	$35.00	$35.00
7 purchase totals =	$666.81		$718.5817	$718.59	$718.60	$718.60