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	$89.37	12.792%	$100.8022	$100.80	$100.80	$100.80
Purchase #2	$56.64	10.384%	$62.5215	$62.52	$62.50	$62.50
Purchase #3	$164.87	11.413%	$183.6866	$183.69	$183.70	$183.70
Purchase #4	$90.35	6.114%	$95.874	$95.87	$95.85	$95.90
Purchase #5	$156.49	8.296%	$169.4724	$169.47	$169.45	$169.50
Purchase #6	$167.77	5.164%	$176.4336	$176.43	$176.45	$176.40
Purchase #7	$41.25	4.435%	$43.0794	$43.08	$43.10	$43.10
7 purchase totals =	$766.74		$831.8697	$831.86	$831.85	$831.90