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 $242.46   10.696%   $268.3935   $268.39   $268.40   $268.40  
  Purchase #2 $188.88   7.846%   $203.6995   $203.70   $203.70   $203.70  
  Purchase #3 $47.47   12.136%   $53.231   $53.23   $53.25   $53.20  
  Purchase #4 $60.36   10.491%   $66.6924   $66.69   $66.70   $66.70  
  Purchase #5 $127.26   10.190%   $140.2278   $140.23   $140.25   $140.20  
  Purchase #6 $182.85   12.367%   $205.4631   $205.46   $205.45   $205.50  
  Purchase #7 $27.49   12.359%   $30.8875   $30.89   $30.90   $30.90  
  7 purchase totals = $876.77       $968.5948   $968.59   $968.65   $968.60