The allowable tolerances for decimal dimensions are wholly decided by how many decimal places are shown in the nominal dimension. Unlike fractions which are decided by being whole numbers or by the denominator in the fraction.
For decimals the chart explains what tolerance can be applied.
So for an example, a number such as 6.695 would have a tolerance of +/- .005 which would result in a minimum of 6.690″ and a maximum of 6.670.
Be aware of questions that ask for a minimum, maximum, range, or tolerance. The Minimum allowed is 6.690″ the maximum is 6.670, the range is 6.695″ to 6.670″, and the tolerance is +/- .005″
Keep your eye on what you are being asked.