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	$130.85	9.652%	$143.4796	$143.48	$143.50	$143.50
Purchase #2	$248.82	3.533%	$257.6108	$257.61	$257.60	$257.60
Purchase #3	$62.90	11.816%	$70.3323	$70.33	$70.35	$70.30
Purchase #4	$98.88	13.253%	$111.9846	$111.98	$112.00	$112.00
Purchase #5	$119.32	11.537%	$133.0859	$133.09	$133.10	$133.10
Purchase #6	$120.51	10.359%	$132.9936	$132.99	$133.00	$133.00
Purchase #7	$89.95	12.160%	$100.8879	$100.89	$100.90	$100.90
7 purchase totals =	$871.23		$950.3747	$950.37	$950.45	$950.40