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 $239.68   8.659%   $260.4339   $260.43   $260.45   $260.40  
  Purchase #2 $247.93   5.524%   $261.6257   $261.63   $261.65   $261.60  
  Purchase #3 $224.99   9.643%   $246.6858   $246.69   $246.70   $246.70  
  Purchase #4 $55.51   5.641%   $58.6413   $58.64   $58.65   $58.60  
  Purchase #5 $98.97   4.134%   $103.0614   $103.06   $103.05   $103.10  
  Purchase #6 $126.26   3.261%   $130.3773   $130.38   $130.40   $130.40  
  Purchase #7 $43.40   4.696%   $45.4381   $45.44   $45.45   $45.40  
  7 purchase totals = $1,036.74       $1,106.2635   $1,106.27   $1,106.35   $1,106.20