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 $248.50   5.110%   $261.1984   $261.20   $261.20   $261.20  
  Purchase #2 $86.45   10.557%   $95.5765   $95.58   $95.60   $95.60  
  Purchase #3 $35.90   9.335%   $39.2513   $39.25   $39.25   $39.30  
  Purchase #4 $196.71   6.237%   $208.9788   $208.98   $209.00   $209.00  
  Purchase #5 $150.96   3.652%   $156.4731   $156.47   $156.45   $156.50  
  Purchase #6 $24.87   6.545%   $26.4977   $26.50   $26.50   $26.50  
  Purchase #7 $210.91   8.411%   $228.6496   $228.65   $228.65   $228.60  
  7 purchase totals = $954.30       $1,016.6254   $1,016.63   $1,016.65   $1,016.70