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	$50.91	10.242%	$56.1242	$56.12	$56.10	$56.10
Purchase #2	$136.92	4.427%	$142.9814	$142.98	$143.00	$143.00
Purchase #3	$81.37	12.520%	$91.5575	$91.56	$91.55	$91.60
Purchase #4	$15.95	11.726%	$17.8203	$17.82	$17.80	$17.80
Purchase #5	$62.32	6.639%	$66.4574	$66.46	$66.45	$66.50
Purchase #6	$49.44	6.377%	$52.5928	$52.59	$52.60	$52.60
Purchase #7	$74.43	3.842%	$77.2896	$77.29	$77.30	$77.30
7 purchase totals =	$471.34		$504.8232	$504.82	$504.80	$504.90