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 $58.94   12.313%   $66.1973   $66.20   $66.20   $66.20  
  Purchase #2 $179.64   10.470%   $198.4483   $198.45   $198.45   $198.40  
  Purchase #3 $247.63   5.682%   $261.7003   $261.70   $261.70   $261.70  
  Purchase #4 $107.33   9.126%   $117.1249   $117.12   $117.10   $117.10  
  Purchase #5 $187.95   10.848%   $208.3388   $208.34   $208.35   $208.30  
  Purchase #6 $60.62   4.529%   $63.3655   $63.37   $63.35   $63.40  
  Purchase #7 $18.49   12.648%   $20.8286   $20.83   $20.85   $20.80  
  7 purchase totals = $860.60       $936.0037   $936.01   $936.00   $935.90