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	$69.86	3.352%	$72.2017	$72.20	$72.20	$72.20
Purchase #2	$60.51	10.443%	$66.8291	$66.83	$66.85	$66.80
Purchase #3	$48.73	8.349%	$52.7985	$52.80	$52.80	$52.80
Purchase #4	$89.78	7.874%	$96.8493	$96.85	$96.85	$96.80
Purchase #5	$92.50	13.284%	$104.7877	$104.79	$104.80	$104.80
Purchase #6	$35.59	12.516%	$40.0444	$40.04	$40.05	$40.00
Purchase #7	$187.59	12.287%	$210.6392	$210.64	$210.65	$210.60
7 purchase totals =	$584.56		$644.1499	$644.15	$644.20	$644.00