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	$231.97	10.477%	$256.2735	$256.27	$256.25	$256.30
Purchase #2	$175.61	6.505%	$187.0334	$187.03	$187.05	$187.00
Purchase #3	$85.85	5.318%	$90.4155	$90.42	$90.40	$90.40
Purchase #4	$59.64	3.303%	$61.6099	$61.61	$61.60	$61.60
Purchase #5	$212.69	8.836%	$231.4833	$231.48	$231.50	$231.50
Purchase #6	$65.31	10.276%	$72.0213	$72.02	$72.00	$72.00
Purchase #7	$51.59	12.300%	$57.9356	$57.94	$57.95	$57.90
7 purchase totals =	$882.66		$956.7725	$956.77	$956.75	$956.70