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	$105.66	8.349%	$114.4816	$114.48	$114.50	$114.50
Purchase #2	$120.89	9.824%	$132.7662	$132.77	$132.75	$132.80
Purchase #3	$32.50	11.300%	$36.1725	$36.17	$36.15	$36.20
Purchase #4	$97.88	5.554%	$103.3163	$103.32	$103.30	$103.30
Purchase #5	$112.74	12.145%	$126.4323	$126.43	$126.45	$126.40
Purchase #6	$63.57	4.671%	$66.5394	$66.54	$66.55	$66.50
Purchase #7	$92.54	8.682%	$100.5743	$100.57	$100.55	$100.60
7 purchase totals =	$625.78		$680.2826	$680.28	$680.25	$680.30