Splitting a big Power Trace to several smaller
2mm trace is about 78mil.
For an external trace carrying 5A that heats up by 20.2 K.
Assuming you mis-etch by 10%, leaves &gt;= 70mil.
With 6A gives a rise of 31.8 K.
So at ambient of 30degrees C a single 2mm trace on top or bottom carrying 6A with good enough manual etching will become about 62 degrees Celcius.
That may not be very good for a precision board, but it's not dangerous. So it'd be good to split it over 3 traces that are within 25% of the same length, but especially if they are short and connected to fatter traces, their heat will also be wicked away. If you make it 1cm between large traces that are 0.75mm or more wide, you will not see much extra heating at all from a single 2mm trace. But it is better to have a main trace &gt;4mm wide and two or more 2mm traces, to reduce the voltage drop.
For reference, the estimated voltage drops for 10cm of trace at several widths with 6A (I use 6A because you say ~5A and it's better to use too much than too little):

2mm: 0.111V (heating =~ 26K)
3mm: 0.072V (heating =~ 20K)
4mm: 0.052V (heating =~ 14.5K)
5mm: 0.041V (heating =~ 12 K)

So, depending on the length you may already be overestimating the need for a certain size of traces.
This does assume the final trace is the size stated with slightly under etched sides, so if you manually etch take a decent margin. I.e. if 3mm would be acceptable it's good to use 4mm, etc.
EDIT, by request:
If you have no engineering handbook for electronics design with all the normal, integral and differential maths to do with anything ever, you can also use the Saturn PCB tool to calculate numbers like the above ones, which I used in this case, because I didn't want to spend too much time on it:
The Saturn PCB tool, free download from http://saturnpcb.com