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	$232.60	9.748%	$255.2738	$255.27	$255.25	$255.30
Purchase #2	$238.78	11.235%	$265.6069	$265.61	$265.60	$265.60
Purchase #3	$21.76	7.677%	$23.4305	$23.43	$23.45	$23.40
Purchase #4	$27.32	7.507%	$29.3709	$29.37	$29.35	$29.40
Purchase #5	$134.64	12.356%	$151.2761	$151.28	$151.30	$151.30
Purchase #6	$27.47	9.841%	$30.1733	$30.17	$30.15	$30.20
Purchase #7	$138.78	10.168%	$152.8912	$152.89	$152.90	$152.90
7 purchase totals =	$821.35		$908.0227	$908.02	$908.00	$908.10