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	$77.90	9.460%	$85.2693	$85.27	$85.25	$85.30
Purchase #2	$231.86	11.697%	$258.9807	$258.98	$259.00	$259.00
Purchase #3	$56.29	9.243%	$61.4929	$61.49	$61.50	$61.50
Purchase #4	$117.97	5.729%	$124.7285	$124.73	$124.75	$124.70
Purchase #5	$157.95	13.695%	$179.5813	$179.58	$179.60	$179.60
Purchase #6	$51.65	4.725%	$54.0905	$54.09	$54.10	$54.10
Purchase #7	$77.86	9.842%	$85.523	$85.52	$85.50	$85.50
7 purchase totals =	$771.48		$849.6662	$849.66	$849.70	$849.70