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	$240.61	10.356%	$265.5276	$265.53	$265.55	$265.50
Purchase #2	$215.27	12.154%	$241.4339	$241.43	$241.45	$241.40
Purchase #3	$196.64	13.279%	$222.7518	$222.75	$222.75	$222.80
Purchase #4	$112.62	9.635%	$123.4709	$123.47	$123.45	$123.50
Purchase #5	$48.84	6.252%	$51.8935	$51.89	$51.90	$51.90
Purchase #6	$49.59	9.519%	$54.3105	$54.31	$54.30	$54.30
Purchase #7	$22.89	5.208%	$24.0821	$24.08	$24.10	$24.10
7 purchase totals =	$886.46		$983.4703	$983.46	$983.50	$983.50