Here's how I do it

//-----------------------------------------------------------------------------
// TIMER2_ISR
//-----------------------------------------------------------------------------
//
// Return Value : None
// Parameters   : None
//
// This is the ISR for the TIMER2.  
//
//-----------------------------------------------------------------------------
void ONE_KHZ_ISR (void) interrupt 5 {
    TF2 = 0;                            // Reset Interrupt


    WDTCN = 0xA5;  //this is not ideal but needed here for other reasons.
    gui_mSecCount++;
    gb_mSecTick = TRUE;
	guc_LCD_delay_mSec--;
}



 

then in my main() function

 while(1){
	

        if (gb_mSecTick == TRUE) {
            gb_mSecTick = FALSE;
            fun1mSec();
        }
        

        if (gb_10mSecTick == TRUE) {
            gb_10mSecTick = FALSE;
            fun10mSec();
        }


        if (gb_100mSecTick == TRUE) {
            gb_100mSecTick = FALSE;
            fun100mSec();
        }


        if (gb_250mSecTick == TRUE) {
            gb_250mSecTick = FALSE;
            fun250mSec();
        }


        if (gb_SecTick == TRUE) {
            gb_SecTick = FALSE;
            fun1Sec();
        }
        
        if (gb_MinTick == TRUE) {

            gb_MinTick = FALSE;
            fun1Min();
        }

    }
}





//this function carries out the period timed functions
//that are not time critical.
void fun1mSec(void) {
    //kick the dog
    if (gui_mSecCount % 10 == 0){
       gb_10mSecTick = TRUE;
    }


    if (gui_mSecCount % 100 == 0){
        gb_100mSecTick = TRUE;
    }
    
    if (gui_mSecCount % 250 == 0){
        gb_250mSecTick = TRUE;
    }


    if (gui_mSecCount % 1000 == 0){
        gb_SecTick = TRUE;
    }



    if (gui_mSecCount >=60000){
        gui_mSecCount = 0;   
        gb_MinTick = TRUE;
    
    }

}
 .... and so on




 

These are not time critical values, here, they are ABOUT the time period you expect, for time critical functions you can use the other timers. not associated with your tick function