[paledot]

When I've encountered it, the interface has looked like this (as I'm in the process of filling it in):

    $_.__
    $_._1
    $_.12
    $1.23
    $12.34

Typically it also rejects non-numeral inputs, so if you muscle-memory a decimal point it gets ignored and your input (hopefully) proceeds normally. Whereas a "left-aligned" input would be the style that we're accustomed to from general text input:

    $
    $1
    $12
    $12.
    $12.3
    $12.34