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	$85.40	4.550%	$89.2857	$89.29	$89.30	$89.30
Purchase #2	$131.29	9.181%	$143.3437	$143.34	$143.35	$143.30
Purchase #3	$29.38	7.370%	$31.5453	$31.55	$31.55	$31.50
Purchase #4	$12.56	8.667%	$13.6486	$13.65	$13.65	$13.60
Purchase #5	$241.61	5.108%	$253.9514	$253.95	$253.95	$254.00
Purchase #6	$103.97	12.859%	$117.3395	$117.34	$117.35	$117.30
Purchase #7	$199.56	7.462%	$214.4512	$214.45	$214.45	$214.50
7 purchase totals =	$803.77		$863.5654	$863.57	$863.60	$863.50