Yes, it is allowable to refuse to give money to panhandlers, especially to those who do not appear to need it or who appear as though they would waste it. If there is not a question of personal safety, you could politely offer them information on how to locate the nearest homeless shelter. Since you regularly meet panhandlers in the course of your daily life, you might ask a nearby shelter for business cards with the shelter’s contact information that you could distribute instead of money.
In any event, if you meet your obligation to support the Church and to support those less fortunate than yourself by giving to reputable charities, you need have no qualms about gently refusing to give spare change to panhandlers.