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	$237.77	11.133%	$264.2409	$264.24	$264.25	$264.20
Purchase #2	$48.83	5.709%	$51.6177	$51.62	$51.60	$51.60
Purchase #3	$133.32	3.477%	$137.9555	$137.96	$137.95	$138.00
Purchase #4	$169.59	10.591%	$187.5513	$187.55	$187.55	$187.60
Purchase #5	$103.28	13.264%	$116.9791	$116.98	$117.00	$117.00
Purchase #6	$17.46	3.568%	$18.083	$18.08	$18.10	$18.10
Purchase #7	$158.90	13.602%	$180.5136	$180.51	$180.50	$180.50
7 purchase totals =	$869.15		$956.9411	$956.94	$956.95	$957.00