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	$94.32	11.679%	$105.3356	$105.34	$105.35	$105.30
Purchase #2	$164.42	8.838%	$178.9514	$178.95	$178.95	$179.00
Purchase #3	$223.87	8.164%	$242.1467	$242.15	$242.15	$242.10
Purchase #4	$50.30	12.349%	$56.5115	$56.51	$56.50	$56.50
Purchase #5	$18.49	12.751%	$20.8477	$20.85	$20.85	$20.80
Purchase #6	$86.60	4.481%	$90.4805	$90.48	$90.50	$90.50
Purchase #7	$105.82	11.105%	$117.5713	$117.57	$117.55	$117.60
7 purchase totals =	$743.82		$811.8447	$811.85	$811.85	$811.80