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	$158.96	5.694%	$168.0112	$168.01	$168.00	$168.00
Purchase #2	$105.44	6.154%	$111.9288	$111.93	$111.95	$111.90
Purchase #3	$127.30	9.579%	$139.4941	$139.49	$139.50	$139.50
Purchase #4	$124.78	7.645%	$134.3194	$134.32	$134.30	$134.30
Purchase #5	$146.87	10.147%	$161.7729	$161.77	$161.75	$161.80
Purchase #6	$232.69	10.286%	$256.6245	$256.62	$256.60	$256.60
Purchase #7	$105.97	10.348%	$116.9358	$116.94	$116.95	$116.90
7 purchase totals =	$1,002.01		$1,089.0867	$1,089.08	$1,089.05	$1,089.00