ROUND
Returns a numeric expression, rounded to the specified length or precision.

Syntax
ROUND ( numeric_expression , length [ , function ] )

Arguments
numeric_expression

Is an expression of the exact numeric or approximate numeric data type category, except for the bit data type.

length

Is the precision to which numeric_expression is to be rounded. length must be tinyint, smallint, or int. When length is a positive number, numeric_expression is rounded to the number of decimal places specified by length. When length is a negative number, numeric_expression is rounded on the left side of the decimal point, as specified by length.

function

Is the type of operation to perform. function must be tinyint, smallint, or int. When function is omitted or has a value of 0 (default), numeric_expression is rounded. When a value other than 0 is specified, numeric_expression is truncated.

Return Types
Returns the same type as numeric_expression.

When function is omitted or has a value of 0 (default), numeric_expression is rounded. When a value other than 0 is specified, numeric_expression is truncated.
Если 0 или пропущена - выражение округляется. Если не ноль - усекается. Там даже примеры есть...
Зы. Если б писать запоросы было б так просто, как цитировать БОЛ