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	$249.28	3.462%	$257.9101	$257.91	$257.90	$257.90
Purchase #2	$20.83	3.350%	$21.5278	$21.53	$21.55	$21.50
Purchase #3	$12.34	11.429%	$13.7503	$13.75	$13.75	$13.80
Purchase #4	$37.82	7.830%	$40.7813	$40.78	$40.80	$40.80
Purchase #5	$140.96	13.836%	$160.4632	$160.46	$160.45	$160.50
Purchase #6	$245.57	7.466%	$263.9043	$263.90	$263.90	$263.90
Purchase #7	$35.58	3.724%	$36.905	$36.91	$36.90	$36.90
7 purchase totals =	$742.38		$795.2420	$795.24	$795.25	$795.30