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 $250.80   7.227%   $268.9253   $268.93   $268.95   $268.90  
  Purchase #2 $23.74   10.669%   $26.2728   $26.27   $26.25   $26.30  
  Purchase #3 $61.32   8.401%   $66.4715   $66.47   $66.45   $66.50  
  Purchase #4 $183.89   12.309%   $206.525   $206.53   $206.55   $206.50  
  Purchase #5 $203.99   10.274%   $224.9479   $224.95   $224.95   $224.90  
  Purchase #6 $76.34   13.815%   $86.8864   $86.89   $86.90   $86.90  
  Purchase #7 $69.39   4.709%   $72.6576   $72.66   $72.65   $72.70  
  7 purchase totals = $869.47       $952.6865   $952.70   $952.70   $952.70