To calculate a running total that resets at the start of each quarter, you can use CALCULATE and FILTER in DAX while leveraging the DATESQTD function for quarter-based calculations.
DAX Measure for Running Total (Quarterly Reset)
RunningTotal_Quarterly =  
CALCULATE(  
    SUM( 'Sales'[Amount] ),  
    FILTER(  
        ALLSELECTED( 'Sales' ),  
        'Sales'[Date] >= STARTOFQUARTER( 'Sales'[Date] ) &&  
        'Sales'[Date] <= MAX( 'Sales'[Date] )  
    )  
)
Explanation
- ALLSELECTED('Sales') ensures that the measure respects slicers but still evaluates the full date range within the selected period.
- STARTOFQUARTER('Sales'[Date]) determines the first date of the current quarter.
- FILTER ensures that the sum includes all dates from the quarter start up to the current date in context.
Alternative Approach Using TIME INTELLIGENCE
If you have a separate Date Table, use DATESQTD for better time intelligence support:
RunningTotal_Quarterly =  
TOTALQTD( SUM('Sales'[Amount]), 'Date'[Date] )