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	$74.44	10.566%	$82.3053	$82.31	$82.30	$82.30
Purchase #2	$46.37	9.710%	$50.8725	$50.87	$50.85	$50.90
Purchase #3	$154.86	13.602%	$175.9241	$175.92	$175.90	$175.90
Purchase #4	$49.25	10.312%	$54.3287	$54.33	$54.35	$54.30
Purchase #5	$180.68	5.361%	$190.3663	$190.37	$190.35	$190.40
Purchase #6	$43.57	5.604%	$46.0117	$46.01	$46.00	$46.00
Purchase #7	$224.57	3.326%	$232.0392	$232.04	$232.05	$232.00
7 purchase totals =	$773.74		$831.8478	$831.85	$831.80	$831.80