How can I adjust the third decimal of my order total value to always be zero?

[Saifr]

when order comes to my website there are 3 decimal number as example 22.145 What I want is that the third decimal to be always zero as example if it was 22.146 to be 22.150 another example if it was 22.143 to be 22.140

changing product price isn't a solution as I give customers discount code (7-10% off )