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	$132.45	3.466%	$137.0407	$137.04	$137.05	$137.00
Purchase #2	$43.46	11.324%	$48.3814	$48.38	$48.40	$48.40
Purchase #3	$123.46	11.736%	$137.9493	$137.95	$137.95	$137.90
Purchase #4	$98.77	13.254%	$111.861	$111.86	$111.85	$111.90
Purchase #5	$106.55	6.718%	$113.708	$113.71	$113.70	$113.70
Purchase #6	$69.68	11.363%	$77.5977	$77.60	$77.60	$77.60
Purchase #7	$17.28	13.109%	$19.5452	$19.55	$19.55	$19.50
7 purchase totals =	$591.65		$646.0833	$646.09	$646.10	$646.00