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 $91.83   7.404%   $98.6291   $98.63   $98.65   $98.60  
  Purchase #2 $244.56   5.189%   $257.2502   $257.25   $257.25   $257.30  
  Purchase #3 $196.67   3.459%   $203.4728   $203.47   $203.45   $203.50  
  Purchase #4 $228.74   8.103%   $247.2748   $247.27   $247.25   $247.30  
  Purchase #5 $62.90   4.837%   $65.9425   $65.94   $65.95   $65.90  
  Purchase #6 $227.59   13.663%   $258.6856   $258.69   $258.70   $258.70  
  Purchase #7 $179.90   8.484%   $195.1627   $195.16   $195.15   $195.20  
  7 purchase totals = $1,232.19       $1,326.4177   $1,326.41   $1,326.40   $1,326.50