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	$13.82	9.579%	$15.1438	$15.14	$15.15	$15.10
Purchase #2	$210.40	5.762%	$222.5232	$222.52	$222.50	$222.50
Purchase #3	$143.91	5.782%	$152.2309	$152.23	$152.25	$152.20
Purchase #4	$18.37	3.839%	$19.0752	$19.08	$19.10	$19.10
Purchase #5	$102.89	11.577%	$114.8016	$114.80	$114.80	$114.80
Purchase #6	$146.98	5.706%	$155.3667	$155.37	$155.35	$155.40
Purchase #7	$182.54	3.209%	$188.3977	$188.40	$188.40	$188.40
7 purchase totals =	$818.91		$867.5391	$867.54	$867.55	$867.50