Custom number formatting which limits decimals, but prevents Rounding to zero

[StrawberryDreams]

How do you go about creating custom and or conditional number formatting which will limit the amount of decimals to be displayed, but allow the full entered amount as is, if the decimals either round to Zero, or won't fit into the cell and give ###### -( and in those cases possibly auto reduce font size to fit ) then return font size to cell when cleared.. Here is a chart with some conditions . If this has been answered and someone has a link that would be great too.

Basic data calculator test 4.xlsm
	E	F	G	H	I
5		Values as entered	Value displayed	Value I want displayed
6		4	4.00%	4%	if no decimal display as single integer
7		5	5.00%	5%	if no decimal display as single integer
8		12.1	12.10%	12.1 %	If one decimal point just display one / don't add a zero
9		0.00009	0.00%	0.00009 %	Don’t' round to zero and rather just display fully . If there are too many decimals to fit into cell and prevent ##### from appearing then auto reduce font size to fit, but don’t increase row height. But return font size back when cell is cleared.
10		5.09	5.09%	5.09%	Show two decimals if last one is not a zero
11		0.1	0.10%	0.1 %	Don't show zero
12		0.01	0.01%	0.01%	Show two decimals if last one is not a zero
13		0.003	0.00%	0.003%	Don't round decimal points to zero
14
Sheet6

Cell Formulas
Range	Formula
H8	H8	=12.1 &" %"
H9	H9	=0.00009 &" %"
H11	H11	=0.1 & " %"
H12	H12	=G12
H13	H13	=0.003 & "%"

 

[StrawberryDreams]

Would you just write a bunch of different conditions in the conditional formatting formula pane ? Such as counting the number of decimals then selecting the appropriate number format and font size ?

maybe something like this:
=LEN(RIGHT(F6,LEN(F6)-FIND(".",F6)))

 

[StrawberryDreams]

maybe something like this:
=IFERROR(LEN(RIGHT(F6,LEN(F6)-FIND(".",F6))),0)

if no decimal then it will give a 0, otherwise it will count the number of decimals.
Then I plug this formula into a helper column , and do conditional formatting based on the helper column result but apply it to the F column...