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 $73.62   11.749%   $82.2696   $82.27   $82.25   $82.30  
  Purchase #2 $98.92   7.326%   $106.1669   $106.17   $106.15   $106.20  
  Purchase #3 $216.64   11.617%   $241.8071   $241.81   $241.80   $241.80  
  Purchase #4 $201.54   8.119%   $217.903   $217.90   $217.90   $217.90  
  Purchase #5 $136.68   7.156%   $146.4608   $146.46   $146.45   $146.50  
  Purchase #6 $246.75   5.162%   $259.4872   $259.49   $259.50   $259.50  
  Purchase #7 $174.91   4.175%   $182.2125   $182.21   $182.20   $182.20  
  7 purchase totals = $1,149.06       $1,236.3071   $1,236.31   $1,236.25   $1,236.40