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 $49.95   11.134%   $55.5114   $55.51   $55.50   $55.50  
  Purchase #2 $240.64   4.873%   $252.3664   $252.37   $252.35   $252.40  
  Purchase #3 $51.62   8.870%   $56.1987   $56.20   $56.20   $56.20  
  Purchase #4 $61.58   9.790%   $67.6087   $67.61   $67.60   $67.60  
  Purchase #5 $13.45   4.567%   $14.0643   $14.06   $14.05   $14.10  
  Purchase #6 $110.55   3.744%   $114.689   $114.69   $114.70   $114.70  
  Purchase #7 $35.87   13.406%   $40.6787   $40.68   $40.70   $40.70  
  7 purchase totals = $563.66       $601.1172   $601.12   $601.10   $601.20