rounding off, roundoff,でもいいとおもいます。Truncateはただ切り捨てることです。round up は切り上げです。

Round offは動詞です。"round (round off) the figure to one decimal place"は「小数点第二位を四捨五入」にあたります。

"round off the second decimal place"も同じ意味です。

In general, "rounding" would be used. However, that term has been extended to include other algoithms, as described below. To indicate the specific method inherent in the Japanese term, the English expression "round to higher nearest" can be used.

The following explanation is found at http://www.brianhetrick.com/casio/gmround.html

Rounding a numeric quantity to the nearest specified digits place is finding the closest value whose decimal representation ends at the specified digits place. For example, 1.573329 rounds to 2, 1.6, 1.57, 1.573, 1.5733, or 1.57333 as the rounding occurs to the units, tenths, hundredths, thousandths, ten thousandths, or hundred thousandths place.

When a quantity is exactly half way between two available values, the direction in which to round is not obvious. Typically, rounding takes place to the available value farther away from zero. This is called round to higher nearest, and is generally the rounding method taught in primary school. However, rounding to the value with an even last digit has better error properties. This is called round to even nearest, and is generally the rounding method used in statistics and finance.

Two other operations are sometimes desired: choosing the closer to zero of the two nearest values whose decimal representation ends at a specified digits place, or choosing the farther from zero of the two values. These operations are not necessarily rounding, as the closer of the two values to the value being 途ounded

"fractions over 1/2 (inclusive) as one" can be expressed as "rounding up".

standard rounding以外に commercial rounding, scientific rounding, truncationなどがありそれぞれ異なります。詳細はhttp://www.trans-mart.net（翻訳サイトトランスマート）の投稿欄「メンバーズカフェ」に説明があります。