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 $245.67   6.320%   $261.1963   $261.20   $261.20   $261.20  
  Purchase #2 $64.78   3.248%   $66.8841   $66.88   $66.90   $66.90  
  Purchase #3 $186.55   7.871%   $201.2334   $201.23   $201.25   $201.20  
  Purchase #4 $45.94   6.477%   $48.9155   $48.92   $48.90   $48.90  
  Purchase #5 $193.38   11.354%   $215.3364   $215.34   $215.35   $215.30  
  Purchase #6 $101.57   4.650%   $106.293   $106.29   $106.30   $106.30  
  Purchase #7 $31.92   11.439%   $35.5713   $35.57   $35.55   $35.60  
  7 purchase totals = $869.81       $935.4300   $935.43   $935.45   $935.40