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 $183.32   12.715%   $206.6291   $206.63   $206.65   $206.60  
  Purchase #2 $242.66   4.619%   $253.8685   $253.87   $253.85   $253.90  
  Purchase #3 $250.59   12.383%   $281.6206   $281.62   $281.60   $281.60  
  Purchase #4 $194.89   7.206%   $208.9338   $208.93   $208.95   $208.90  
  Purchase #5 $125.84   11.846%   $140.747   $140.75   $140.75   $140.70  
  Purchase #6 $178.55   10.293%   $196.9282   $196.93   $196.95   $196.90  
  Purchase #7 $60.83   9.535%   $66.6301   $66.63   $66.65   $66.60  
  7 purchase totals = $1,236.68       $1,355.3573   $1,355.36   $1,355.40   $1,355.20