(HasOpportunityLineItem &&
(ISCHANGED( Total_List_Price__c))  ||
(ISCHANGED( Total_End_User_Price__c)) ||
(ISCHANGED( Total_End_User_Price_Discount__c)) ||
(ISCHANGED( Total_Standard_Price__c)) ||
(ISCHANGED( Total_Standard_Price_Discount__c)) ||
(ISCHANGED( Total_SPR_Price__c)) ||
(ISCHANGED( Total_SPR_Price_Discount__c)) ||
(ISCHANGED( Total_Price__c)) ||
(ISCHANGED( Total_Price_Discount__c)) ||
(ISCHANGED( Total_SPR_Margin__c)) ) &&  dummyCheckbox__c == True

trigger TotalOpportunityProductTrigger on OpportunityLineItem (after insert, after update, after delete) {

Opportunity Oppor = new Opportunity();
LPGCalculatorSettings__c objCalSetting = LPGCalculatorSettings__c.getValues('RollupTriggerSwitch');

if(objCalSetting.value__c){
TotalOpportunityProductTriggerHandler tp = new TotalOpportunityProductTriggerHandler();

if(Trigger.isInsert && Trigger.isAfter){

tp.TotalField(Trigger.new);
oppor.dummyCheckbox__c = False;
}
else if (Trigger.isUpdate && Trigger.isAfter){

tp.TotalField(Trigger.new);
oppor.dummyCheckbox__c = False;
}
else if(Trigger.isDelete && Trigger.isAfter){

tp.TotalField(Trigger.old);
oppor.dummyCheckbox__c = False;
}
}
}

if(Trigger.isInsert && Trigger.isAfter){
//you need to set the checkbox field false here
//but as this code run in After syntax so first you need to query all Opportunity and then set it to false.
// and you need to do this in all if conditions.
tp.TotalField(Trigger.new);

}