[t]o delete the least significant digit or digits of a numeral, and to adjust the part retained in accordance with some rule.
rounding a figure up or down to disguise precise statistics. For example if one table may have a cell with value of 10,000 for all people doing some activity up to the present date. However, the following month, the figure in that cell rises to 10,001. If an intruder compares the tables it would be easy to deduce a cell of 1. Rounding would prevent this.