In your redmine program, find the file
\app\views\issues\_attributes.rthml
The code for setting the increment 10% is on line 38 (Version 1.1.0)
<p><%= f.select :done_ratio, ((0..10).to_a.collect {|r| ["#{r*10} %", r*10] }) %></p>
, 1 10 1, 10 %. , .
, 5%
<p><%= f.select :done_ratio, ((0..10).step(0.5).to_a.collect {|r| ["#{r*10} %", r*10] }) %></p>
Redmine, 0,5, , . , ,
<p><%= f.select :done_ratio, ((0..100).step(5).to_a.collect {|r| ["#{r} %", r] }) %></p>
1% .
\app\views\issues\_form_update.rthml
, .