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	$77.70	5.577%	$82.0333	$82.03	$82.05	$82.00
Purchase #2	$244.29	4.315%	$254.8311	$254.83	$254.85	$254.80
Purchase #3	$25.42	9.271%	$27.7767	$27.78	$27.80	$27.80
Purchase #4	$190.93	9.722%	$209.4922	$209.49	$209.50	$209.50
Purchase #5	$29.86	6.292%	$31.7388	$31.74	$31.75	$31.70
Purchase #6	$63.89	4.124%	$66.5248	$66.52	$66.50	$66.50
Purchase #7	$212.54	5.661%	$224.5719	$224.57	$224.55	$224.60
7 purchase totals =	$844.63		$896.9688	$896.96	$897.00	$896.90