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	$242.64	3.165%	$250.3196	$250.32	$250.30	$250.30
Purchase #2	$32.97	4.725%	$34.5278	$34.53	$34.55	$34.50
Purchase #3	$182.34	13.259%	$206.5165	$206.52	$206.50	$206.50
Purchase #4	$87.47	6.241%	$92.929	$92.93	$92.95	$92.90
Purchase #5	$198.35	8.766%	$215.7374	$215.74	$215.75	$215.70
Purchase #6	$59.89	11.473%	$66.7612	$66.76	$66.75	$66.80
Purchase #7	$95.38	5.106%	$100.2501	$100.25	$100.25	$100.30
7 purchase totals =	$899.04		$967.0416	$967.05	$967.05	$967.00