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 $242.63   7.870%   $261.725   $261.73   $261.75   $261.70  
  Purchase #2 $86.43   4.118%   $89.9892   $89.99   $90.00   $90.00  
  Purchase #3 $93.31   3.557%   $96.629   $96.63   $96.65   $96.60  
  Purchase #4 $105.32   13.391%   $119.4234   $119.42   $119.40   $119.40  
  Purchase #5 $220.93   11.849%   $247.108   $247.11   $247.10   $247.10  
  Purchase #6 $206.75   8.510%   $224.3444   $224.34   $224.35   $224.30  
  Purchase #7 $71.81   11.398%   $79.9949   $79.99   $80.00   $80.00  
  7 purchase totals = $1,027.18       $1,119.2139   $1,119.21   $1,119.25   $1,119.10