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 $37.32   12.351%   $41.9294   $41.93   $41.95   $41.90  
  Purchase #2 $58.54   12.631%   $65.9342   $65.93   $65.95   $65.90  
  Purchase #3 $90.57   8.279%   $98.0683   $98.07   $98.05   $98.10  
  Purchase #4 $240.36   7.175%   $257.6058   $257.61   $257.60   $257.60  
  Purchase #5 $175.26   4.151%   $182.535   $182.54   $182.55   $182.50  
  Purchase #6 $248.92   6.277%   $264.5447   $264.54   $264.55   $264.50  
  Purchase #7 $50.75   5.656%   $53.6204   $53.62   $53.60   $53.60  
  7 purchase totals = $901.72       $964.2378   $964.24   $964.25   $964.10