I understand that it is generally OK to estimate when you are using a calculation to get a Y/N answer (i.e. determining whether to proceed/not proceed based on being above or below a specifc target).

Other than this situation, is it OK to round or estimate your answers to get an approximate answer more quickly? Do I need to ask the interviewer every time I want to round or estimate slightly [e.g. rounding (155 million / 206) to (155 million / 200)]?

Also, if specifc answers are required, what level of precision is generally acceptable? One decimal place?