Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $237.62   7.709%   $255.9381   $255.94   $255.95   $255.90  
  Purchase #2 $155.83   12.114%   $174.7072   $174.71   $174.70   $174.70  
  Purchase #3 $73.99   4.762%   $77.5134   $77.51   $77.50   $77.50  
  Purchase #4 $246.70   13.833%   $280.826   $280.83   $280.85   $280.80  
  Purchase #5 $90.47   8.204%   $97.8922   $97.89   $97.90   $97.90  
  Purchase #6 $234.34   5.314%   $246.7928   $246.79   $246.80   $246.80  
  Purchase #7 $208.28   13.221%   $235.8167   $235.82   $235.80   $235.80  
  7 purchase totals = $1,247.23       $1,369.4864   $1,369.49   $1,369.50   $1,369.40