Rounding decimals (...or custom number formatting?)

I have a spreadsheet that looks something like this:

	A	B	C	D
1	Item Number	Sold Last Week	Sold This Week	Change
2	1100256	968	2455	+153.62%
3	1100257	28	49	+75%
4	1100258	8	9	+12.5%
5	1100259	7300	44	-99.4%

The formula I'm using to get the value in column D is:

=IF((((C2-B2)/B2)*100)>0,(CONCATENATE("+",(ROUND((((C2-B2)/B2)*100),2)),"%")),(CONCATENATE((ROUND((((C2-B2)/B2)*100),2)),"%")))

How can I round the decimals to make sure all my numbers appear with two decimals? Since the formula uses CONCATENATE, I can't simply format the cells to show two decimals.

I want it to look like this:

	A	B	C	D
1	Item Number	Sold Last Week	Sold This Week	Change
2	1100256	968	2455	+153.62%
3	1100257	28	49	+75.00%
4	1100258	8	9	+12.50%
5	1100259	7300	44	-99.40%

If you know a better way of doing this than the solution I'm asking for here, I'm all ears. I bet this might be much easier using custom number formatting. I'm just not well-versed in formatting abilities.