Discounting a third

A common promotion that we run is a third off our products. Unfortunately I am currently unable to deduct a third from any product sold in the discount field.

This current view is in Opportunity / Products Subscription Plans \ Interests \ Select Product \ Edit

See Below:

2018-01-08_10h20_45

2018-01-08_10h20_50

It seems the discount field only likes integers as discounts. Is there any way that this will accept 33.3% if only to one decimal place for more accuracy.

This is obviously skewing our reports quite significantly.