Tapeworms area part of the flea life cycle. If you don't get rid of the fleas on the dog and in the house and yard, you won't break the cycle. Instead of a flea collar, I would go with the topical spot-on formulas such as k-9 advantix II, Frontline Plus or something similar (name brand only). For your home, I would vacuum your house, throw out the bag and put boric acid or food grade (not swimming pool) diatomaceous earth in your carpets or rugs by brushing/brooming it in to them after the vacuuming. These are both less toxic than table salt and will kill the flea larvae in the carpet or rug before they mature. Wash and thoroughly dry all of the dog's bedding and toys that are cloth. I also use Sentinel as a heartworm prevenative since Interceptor was discontinued and it has a flea "birth control" (Program) in it with the heartworm medication.
You never metnioned the name of the medication that you have been giving your dog for the tapeworms. There are two types of tapeworms - one from fleas and one from eating rodents (moles, voles, rabbits, etc.). You may need to give something such as Panacur/Safeguard and another medication with praziquantel in it. It ist he praziquantel that gets the tapeworms that come from fleas.
There are six dogs in my home and no fleas or worms.
Sabra - female GSD - born April 30, 2012
Sargeant - rescued senior GSD male/foster failure - approximately ten years old (August 2013)
Max - rescued GSD - Dec 22, 2010 to March 7, 2012 - at the bridge
Sable - rescued GSD - at the bridge