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 $200.95   3.253%   $207.4869   $207.49   $207.50   $207.50  
  Purchase #2 $247.67   5.764%   $261.9457   $261.95   $261.95   $261.90  
  Purchase #3 $20.90   6.256%   $22.2075   $22.21   $22.20   $22.20  
  Purchase #4 $28.57   13.353%   $32.385   $32.39   $32.40   $32.40  
  Purchase #5 $95.73   8.193%   $103.5732   $103.57   $103.55   $103.60  
  Purchase #6 $61.37   4.159%   $63.9224   $63.92   $63.90   $63.90  
  Purchase #7 $15.90   7.131%   $17.0338   $17.03   $17.05   $17.00  
  7 purchase totals = $671.09       $708.5545   $708.56   $708.55   $708.50