PA60 AIR TAXI CARGO FLT ON VFR FLT PLAN WAS FLYING 10 FT BELOW THE FLOOR OF THE CLASS B AIRSPACE. DEP CTL REQUESTED ALT AND RPTR STATED 3000 FT WHEN HE WAS ACTUALLY AT 2990 FT. FLOOR OF THE CLASS B AIRSPACE IS 3000 FT AND CTLR QUESTIONED WHO CLRED THE FLT INTO THE CLASS B AIRSPACE.

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I WAS FLYING A PA60 VFR FROM TEB TO BDL. I MAINTAINED 1400 FT MSL TO REMAIN CLR OF NEW YORK'S CLASS B AIRSPACE. AFTER PASSING THE ALPINE TWR (TEB VOR/DME 053 DEG RADIAL; 9.0 DME) THE FLOOR OF THE CLASS B AIRSPACE RAISES TO 3000 FT MSL. AFTER PASSING THE ALPINE; I CLBED TO 2990 FT MSL TO REMAIN CLR OF NEW YORK'S CLASS B AIRSPACE AND CLR HPN'S CLASS D AIRSPACE. I TOLD NEW YORK'S APCH CTLR (120.8) WHAT I WAS DOING AND HE GAVE ME A SQUAWK AND REQUESTED MY ALT. NOT THINKING BEFORE I SPOKE; I ROUNDED MY ALT TO THE NEAREST 100 FT (WHICH MOST PLTS DO) AND TOLD HIM I WAS AT 3000 FT. HE ASKED ME WHO CLRED ME INTO THE CLASS B AIRSPACE AND I RESPONDED THAT I WAS NOT IN THE CLASS B AIRSPACE. HE SAID I MOST CERTAINLY WAS AT 3000 FT. THIS IS A NIGHTLY OP FOR OUR CARRIER AND THERE SEEMS TO BE SOME FRICTION BTWN THIS CTLR AND OUR PLANES. I RESPONDED THAT ACCORDING TO MY VFR CHART; I WAS NOT IN THE CLASS B AIRSPACE. I SHOULD HAVE CALMED DOWN AND RESPONDED THAT I WAS AT 2990 FT MSL INSTEAD OF 3000 FT MSL. THE CTLR THEN PROVIDED ME WITH FLT FOLLOWING AFTER HPN.