CORDIC is what many digital calculators use (along with decimal floating point).
Source? I'd find this a bit strange because:
1. I suspect decimal floating point is quite expensive to implement computationally.
2. Not an expert, but I think the floating-point algorithms and proofs for bases other than 2 are less well researched and less well known.
3. A calculator is a resource-constrained device.
4. Are there even any real benefits? Yes, some human-friendly numbers have an exact finite representation that is missing in base-2, but I can't see why would that matter, compared to just using 32-bit or 64-bit IEEE-754.
Hardware with decimal floating-point only appeared in 2007, and still doesn't seem to be easily available:
Decimal, and particularly BCD floating point, is much simpler than binary for a calculator since the numbers don't need any additional conversion steps to display.
And the fact that 0.1 + 0.1 works as expected is indeed a huge benefit.
http://merthsoft.com/linkguide/ti83+/vars.html
In practice, the cost is not that much different because four-function calculators do not do many calculations at once. Even in a graphing calculator, drawing a plot is never slow enough to make the device useless.