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	$29.89	5.204%	$31.4455	$31.45	$31.45	$31.40
Purchase #2	$201.93	11.265%	$224.6774	$224.68	$224.70	$224.70
Purchase #3	$83.43	9.520%	$91.3725	$91.37	$91.35	$91.40
Purchase #4	$53.71	10.451%	$59.3232	$59.32	$59.30	$59.30
Purchase #5	$48.65	8.398%	$52.7356	$52.74	$52.75	$52.70
Purchase #6	$67.43	13.481%	$76.5202	$76.52	$76.50	$76.50
Purchase #7	$49.33	12.832%	$55.66	$55.66	$55.65	$55.70
7 purchase totals =	$534.37		$591.7344	$591.74	$591.70	$591.70