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	$11.35	12.788%	$12.8014	$12.80	$12.80	$12.80
Purchase #2	$160.40	6.810%	$171.3232	$171.32	$171.30	$171.30
Purchase #3	$8.37	4.522%	$8.7485	$8.75	$8.75	$8.70
Purchase #4	$13.93	10.381%	$15.3761	$15.38	$15.40	$15.40
Purchase #5	$60.33	10.384%	$66.5947	$66.59	$66.60	$66.60
Purchase #6	$54.92	5.466%	$57.9219	$57.92	$57.90	$57.90
Purchase #7	$211.90	5.168%	$222.851	$222.85	$222.85	$222.90
7 purchase totals =	$521.20		$555.6168	$555.61	$555.60	$555.60