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	$180.93	3.534%	$187.3241	$187.32	$187.30	$187.30
Purchase #2	$241.72	12.118%	$271.0116	$271.01	$271.00	$271.00
Purchase #3	$221.92	5.709%	$234.5894	$234.59	$234.60	$234.60
Purchase #4	$18.57	8.634%	$20.1733	$20.17	$20.15	$20.20
Purchase #5	$59.26	12.802%	$66.8465	$66.85	$66.85	$66.80
Purchase #6	$159.49	7.795%	$171.9222	$171.92	$171.90	$171.90
Purchase #7	$50.59	11.305%	$56.3092	$56.31	$56.30	$56.30
7 purchase totals =	$932.48		$1,008.1763	$1,008.17	$1,008.10	$1,008.10