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 $238.52   9.744%   $261.7614   $261.76   $261.75   $261.80  
  Purchase #2 $75.29   12.871%   $84.9806   $84.98   $85.00   $85.00  
  Purchase #3 $236.80   7.226%   $253.9112   $253.91   $253.90   $253.90  
  Purchase #4 $24.85   6.288%   $26.4126   $26.41   $26.40   $26.40  
  Purchase #5 $154.27   6.694%   $164.5968   $164.60   $164.60   $164.60  
  Purchase #6 $170.49   13.690%   $193.8301   $193.83   $193.85   $193.80  
  Purchase #7 $55.34   6.531%   $58.9543   $58.95   $58.95   $59.00  
  7 purchase totals = $955.56       $1,044.4470   $1,044.44   $1,044.45   $1,044.50