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	$103.78	12.706%	$116.9663	$116.97	$116.95	$117.00
Purchase #2	$88.69	12.232%	$99.5386	$99.54	$99.55	$99.50
Purchase #3	$18.83	10.549%	$20.8164	$20.82	$20.80	$20.80
Purchase #4	$55.95	10.865%	$62.029	$62.03	$62.05	$62.00
Purchase #5	$15.61	3.448%	$16.1482	$16.15	$16.15	$16.10
Purchase #6	$123.98	3.638%	$128.4904	$128.49	$128.50	$128.50
Purchase #7	$52.66	13.105%	$59.5611	$59.56	$59.55	$59.60
7 purchase totals =	$459.50		$503.5500	$503.56	$503.55	$503.50