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 $58.90   13.588%   $66.9033   $66.90   $66.90   $66.90  
  Purchase #2 $107.81   13.839%   $122.7298   $122.73   $122.75   $122.70  
  Purchase #3 $77.92   10.680%   $86.2419   $86.24   $86.25   $86.20  
  Purchase #4 $42.91   8.719%   $46.6513   $46.65   $46.65   $46.70  
  Purchase #5 $130.71   12.129%   $146.5638   $146.56   $146.55   $146.60  
  Purchase #6 $92.59   10.237%   $102.0684   $102.07   $102.05   $102.10  
  Purchase #7 $198.80   3.518%   $205.7938   $205.79   $205.80   $205.80  
  7 purchase totals = $709.64       $776.9523   $776.94   $776.95   $777.00