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	$109.59	13.120%	$123.9682	$123.97	$123.95	$124.00
Purchase #2	$191.92	12.283%	$215.4935	$215.49	$215.50	$215.50
Purchase #3	$136.49	7.535%	$146.7745	$146.77	$146.75	$146.80
Purchase #4	$56.89	11.574%	$63.4744	$63.47	$63.45	$63.50
Purchase #5	$237.82	7.555%	$255.7873	$255.79	$255.80	$255.80
Purchase #6	$173.82	8.105%	$187.9081	$187.91	$187.90	$187.90
Purchase #7	$112.48	11.271%	$125.1576	$125.16	$125.15	$125.20
7 purchase totals =	$1,019.01		$1,118.5636	$1,118.56	$1,118.50	$1,118.70