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 $92.58   11.527%   $103.2517   $103.25   $103.25   $103.30  
  Purchase #2 $130.65   12.263%   $146.6716   $146.67   $146.65   $146.70  
  Purchase #3 $98.54   11.855%   $110.2219   $110.22   $110.20   $110.20  
  Purchase #4 $113.39   11.270%   $126.1691   $126.17   $126.15   $126.20  
  Purchase #5 $34.90   9.481%   $38.2089   $38.21   $38.20   $38.20  
  Purchase #6 $194.44   6.547%   $207.17   $207.17   $207.15   $207.20  
  Purchase #7 $248.43   5.418%   $261.8899   $261.89   $261.90   $261.90  
  7 purchase totals = $912.93       $993.5831   $993.58   $993.50   $993.70