1234.56789 to 3 significant figures is 1230, but round to 3 digits I would expect to return 1234.568.

If you need to round to significant figures you would need to use: ROUND(A1,3-LEN(INT(A1)))

Assuming your data was in cell A1. Change the 3 (at 3-Len...) to whatever number you wish to use.