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 $46.47   13.262%   $52.6329   $52.63   $52.65   $52.60  
  Purchase #2 $136.80   10.728%   $151.4759   $151.48   $151.50   $151.50  
  Purchase #3 $175.76   3.725%   $182.3071   $182.31   $182.30   $182.30  
  Purchase #4 $24.54   10.581%   $27.1366   $27.14   $27.15   $27.10  
  Purchase #5 $103.92   8.317%   $112.563   $112.56   $112.55   $112.60  
  Purchase #6 $205.48   12.271%   $230.6945   $230.69   $230.70   $230.70  
  Purchase #7 $17.33   12.335%   $19.4677   $19.47   $19.45   $19.50  
  7 purchase totals = $710.30       $776.2777   $776.28   $776.30   $776.30