What is the correct term for this die? It is a standard die in any 7 dice set.
It has multiples of ten from 10 to 00 written on it (10, 20, 30, 40, 50, 60, 70, 80, 90, (1)00).
I seem to think that it is called a 'percentile die', is this correct?
The two ten-sided dice used together to generate a number in the range 1-100 (or 0-99) are percentile dice (plural). The same term is applies to a pair of twenty-sided dice, each marked 0-9 twice, used for the same purpose.
Back in the Before Time, dice sets didn't include a die marked with double-digits; you would just roll different-colored dice, having declared one of them the "tens". I think that sometimes the specific die you are asking about is called the tens die; Chessex calls it a "Tens 10" on their website.
The one with the multiples of 10 on it is often referred to as a "decader" die, at least on crafting sites like etsy and shapeways.