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 $242.99   7.521%   $261.2653   $261.27   $261.25   $261.30  
  Purchase #2 $56.63   3.521%   $58.6239   $58.62   $58.60   $58.60  
  Purchase #3 $161.32   13.285%   $182.7514   $182.75   $182.75   $182.80  
  Purchase #4 $63.44   3.799%   $65.8501   $65.85   $65.85   $65.90  
  Purchase #5 $23.55   13.705%   $26.7775   $26.78   $26.80   $26.80  
  Purchase #6 $244.48   10.777%   $270.8276   $270.83   $270.85   $270.80  
  Purchase #7 $191.90   3.865%   $199.3169   $199.32   $199.30   $199.30  
  7 purchase totals = $984.31       $1,065.4127   $1,065.42   $1,065.40   $1,065.50