Trigger changes a fraction of values after every update

Question

I have written a before update trigger on Opportunity to update some fields based on formula fields.

Due to some limitations, I could not create a formula field so created number fields and populate them using a trigger.

Since the calculation is based on some formula fields, I'm updating the values after every update.

The problem I'm facing is it's changing the value after every save even when I'm not changing any value. Ex: if my earlier value was 19.25 now it's changing it to 19.24.

What I'm guessing is it calculates the value after every save but because of many formulae, it adjusts the value by some fraction.

How can I keep my values as it is if there is not change? I tried comparing old value and new value but in that case it's not updating at all.

for(Opportunity opp : oppList){

    if(opp.Total_Cost_Formula__c != oldMap.get(opp.Id).Total_Cost_Formula__c){
       opp.unit_sales_price__c  = 1.60 * opp.unit_total_cost__c;
    }
}