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	$238.91	11.370%	$266.0741	$266.07	$266.05	$266.10
Purchase #2	$131.60	9.284%	$143.8177	$143.82	$143.80	$143.80
Purchase #3	$127.58	8.867%	$138.8925	$138.89	$138.90	$138.90
Purchase #4	$126.56	3.716%	$131.263	$131.26	$131.25	$131.30
Purchase #5	$34.97	4.329%	$36.4839	$36.48	$36.50	$36.50
Purchase #6	$117.34	12.385%	$131.8726	$131.87	$131.85	$131.90
Purchase #7	$131.46	7.478%	$141.2906	$141.29	$141.30	$141.30
7 purchase totals =	$908.42		$989.6944	$989.68	$989.65	$989.80