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	$24.93	8.828%	$27.1308	$27.13	$27.15	$27.10
Purchase #2	$57.45	4.256%	$59.8951	$59.90	$59.90	$59.90
Purchase #3	$84.89	10.662%	$93.941	$93.94	$93.95	$93.90
Purchase #4	$239.64	7.330%	$257.2056	$257.21	$257.20	$257.20
Purchase #5	$101.61	3.600%	$105.268	$105.27	$105.25	$105.30
Purchase #6	$30.73	3.739%	$31.879	$31.88	$31.90	$31.90
Purchase #7	$112.46	12.389%	$126.3927	$126.39	$126.40	$126.40
7 purchase totals =	$651.71		$701.7122	$701.72	$701.75	$701.70