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	$122.59	4.829%	$128.5099	$128.51	$128.50	$128.50
Purchase #2	$21.26	10.548%	$23.5025	$23.50	$23.50	$23.50
Purchase #3	$240.87	6.477%	$256.4711	$256.47	$256.45	$256.50
Purchase #4	$28.25	11.799%	$31.5832	$31.58	$31.60	$31.60
Purchase #5	$183.89	12.435%	$206.7567	$206.76	$206.75	$206.80
Purchase #6	$30.35	9.616%	$33.2685	$33.27	$33.25	$33.30
Purchase #7	$102.89	13.476%	$116.7555	$116.76	$116.75	$116.80
7 purchase totals =	$730.10		$796.8474	$796.85	$796.80	$797.00