In SQL Server you can use STR function to convert a decimal number to string specifying the total number of digits as well as fractional part and its rounding. In Oracle, you can use TO_CHAR function with the corresponding format.
SQL Server:
-- Leave 1 fractional digit and round the number SELECT STR(123.45, 6, 1); # 123.5 -- Truncate the fractional part and round the number SELECT STR(123.7, 6); # 124
Oracle:
-- Leave 1 fractional digit and round the number SELECT TO_CHAR(123.45, 'FM99999.9') FROM dual; # 123.5 -- Truncate the fractional part and round the number SELECT TO_CHAR(123.7, 'FM999999') FROM dual; # 124
For more information, see SQL Server to Oracle Migration.