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	$103.70	7.789%	$111.7772	$111.78	$111.80	$111.80
Purchase #2	$106.70	7.415%	$114.6118	$114.61	$114.60	$114.60
Purchase #3	$40.55	9.606%	$44.4452	$44.45	$44.45	$44.40
Purchase #4	$238.78	11.376%	$265.9436	$265.94	$265.95	$265.90
Purchase #5	$48.79	7.546%	$52.4717	$52.47	$52.45	$52.50
Purchase #6	$134.82	4.348%	$140.682	$140.68	$140.70	$140.70
Purchase #7	$55.78	6.600%	$59.4615	$59.46	$59.45	$59.50
7 purchase totals =	$729.12		$789.3930	$789.39	$789.40	$789.40