Round to closest integer or closest .5 in Ruby

Maybe the title is confusing, but I will try to explain with examples:

Given a float with precision = 2, I want to be able to round either to its closes integer, or to its closest .5. Examples:

Given: 4.12 --> 4
       4.24 --> 4
       4.25 --> 4.5
       4.33 --> 4.5
       4.53 --> 4.5 
       4.65 --> 4.5 
       4.75 --> 5
       4.84 --> 5

What would be a good way to do this in Ruby?