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 $8.71   9.796%   $9.5632   $9.56   $9.55   $9.60  
  Purchase #2 $230.65   12.602%   $259.7165   $259.72   $259.70   $259.70  
  Purchase #3 $36.89   4.618%   $38.5936   $38.59   $38.60   $38.60  
  Purchase #4 $181.37   11.641%   $202.4833   $202.48   $202.50   $202.50  
  Purchase #5 $59.64   8.393%   $64.6456   $64.65   $64.65   $64.60  
  Purchase #6 $210.49   9.503%   $230.4929   $230.49   $230.50   $230.50  
  Purchase #7 $241.48   8.378%   $261.7112   $261.71   $261.70   $261.70  
  7 purchase totals = $969.23       $1,067.2063   $1,067.20   $1,067.20   $1,067.20