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	$142.37	11.302%	$158.4607	$158.46	$158.45	$158.50
Purchase #2	$143.70	3.579%	$148.843	$148.84	$148.85	$148.80
Purchase #3	$28.35	11.331%	$31.5623	$31.56	$31.55	$31.60
Purchase #4	$26.90	13.797%	$30.6114	$30.61	$30.60	$30.60
Purchase #5	$44.81	5.450%	$47.2521	$47.25	$47.25	$47.30
Purchase #6	$84.42	12.631%	$95.0831	$95.08	$95.10	$95.10
Purchase #7	$69.57	12.289%	$78.1195	$78.12	$78.10	$78.10
7 purchase totals =	$540.12		$589.9321	$589.92	$589.90	$590.00