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Handling decimal rounding in T-SQL can be a bit tricky, especially when dealing with invoices where precision is paramount. There exist a myriad of ways to round numbers in SQL, but we will focus on the ROUND function. ROUND is supported in SQL Server 2012, SQL Server 2014, MySQL 5.6, DB2 10.5, and Azure SQL.

The ROUND function in T-SQL takes two arguments: the number to be rounded and the number of decimal places to which the number should be rounded. For example, ROUND(123.456, 2) would return 123.46. Here is how you would use it in SQL Server:

-- SQL Server code

SELECT ROUND(123.456, 2) AS RoundedValue

The ROUND function behaves similarly in MySQL and DB2. However, in MySQL, if the length argument is negative, the ROUND function will round on the left side of the decimal point. For example, ROUND(123.456, -1) would return 120. Here is an example in MySQL:

-- MySQL code

SELECT ROUND(123.456, -1) AS RoundedValue;

In DB2, the ROUND function behaves slightly differently. If the length argument is omitted, the ROUND function will round to the nearest integer. For example, ROUND(123.456) would return 123. Here is how you would use it in DB2:

-- DB2 code

SELECT ROUND(123.456) FROM SYSIBM.SYSDUMMY1;

In Azure SQL, the ROUND function behaves the same as in SQL Server. However, it's worth noting that Azure SQL also supports the ROUND function in its SQL Data Warehouse. Here's an example of how you'd use it:

-- Azure SQL code

SELECT ROUND(123.456, 2) AS RoundedValue;

In conclusion, while there are several ways to handle decimal rounding in T-SQL for invoices, the ROUND function presents a straightforward and supported solution across multiple SQL technologies. As always, be sure to thoroughly test any changes in your rounding approach to ensure accuracy in your invoice calculations.