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	$221.41	4.490%	$231.3513	$231.35	$231.35	$231.40
Purchase #2	$76.67	4.650%	$80.2352	$80.24	$80.25	$80.20
Purchase #3	$43.85	3.536%	$45.4005	$45.40	$45.40	$45.40
Purchase #4	$151.87	5.516%	$160.2471	$160.25	$160.25	$160.20
Purchase #5	$7.67	12.704%	$8.6444	$8.64	$8.65	$8.60
Purchase #6	$242.60	4.407%	$253.2914	$253.29	$253.30	$253.30
Purchase #7	$57.41	4.370%	$59.9188	$59.92	$59.90	$59.90
7 purchase totals =	$801.48		$839.0887	$839.09	$839.10	$839.00