The ppm window depends on your instrument accuray. For a TOF, 10-30 ppm would be normal.
However, the result of a database search by exact mass should only be considered a putative ID.
Even with 0 ppm mass deviation, the correct ID has to be verified by MS/MS and retention time of a standard.
e.g., a METLIN search for m/z 181.0707, [M+H]+ only, will result in 19 hits with 0 ppm.