I generally use an Expression component for rounding (or embed the expression in an output parameter). Using text as floating point input to downstream components can be slow if you’re dealing with large amounts of data.
Here’s a comparison rounding 1,000,000 random numbers on my old iMac running Rhino V7.
Not as slow on a PC with comparable hardware specs also running V7.
The iMac performs much better with the V8 WIP.
Running the V8 WIP on the PC, using the Format component is actually faster than using an Expression 
-Kevin