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 $60.53   7.691%   $65.1854   $65.19   $65.20   $65.20  
  Purchase #2 $93.55   8.827%   $101.8077   $101.81   $101.80   $101.80  
  Purchase #3 $69.42   13.507%   $78.7966   $78.80   $78.80   $78.80  
  Purchase #4 $51.42   6.464%   $54.7438   $54.74   $54.75   $54.70  
  Purchase #5 $234.83   11.744%   $262.4084   $262.41   $262.40   $262.40  
  Purchase #6 $98.88   6.822%   $105.6256   $105.63   $105.65   $105.60  
  Purchase #7 $222.66   13.384%   $252.4608   $252.46   $252.45   $252.50  
  7 purchase totals = $831.29       $921.0283   $921.04   $921.05   $921.00