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 $99.44   6.156%   $105.5615   $105.56   $105.55   $105.60  
  Purchase #2 $49.95   13.465%   $56.6758   $56.68   $56.70   $56.70  
  Purchase #3 $207.48   13.523%   $235.5375   $235.54   $235.55   $235.50  
  Purchase #4 $71.84   13.670%   $81.6605   $81.66   $81.65   $81.70  
  Purchase #5 $228.70   12.134%   $256.4505   $256.45   $256.45   $256.50  
  Purchase #6 $76.33   8.674%   $82.9509   $82.95   $82.95   $83.00  
  Purchase #7 $201.95   6.228%   $214.5274   $214.53   $214.55   $214.50  
  7 purchase totals = $935.69       $1,033.3641   $1,033.37   $1,033.40   $1,033.50