I'm not aware of any significant error rate in the TA cloning step itself. If anything the errors would be more likely to have occurred during the PCR amplification step. What polymerase are you using and what sort of sequence are you amplifying (are there repeats, etc...)?
I am using the BIOTaq DNA polimerase. I know that there are more faithful polymerases, but I need one that leaves an adenine overhang, in order to do TA cloning.
And the sequence which I want to analyze has a copy number polymorphism, I want to sequence the different copies, independently.