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 $24.75   3.496%   $25.6153   $25.62   $25.60   $25.60  
  Purchase #2 $51.87   12.220%   $58.2085   $58.21   $58.20   $58.20  
  Purchase #3 $85.38   8.856%   $92.9413   $92.94   $92.95   $92.90  
  Purchase #4 $156.41   12.303%   $175.6531   $175.65   $175.65   $175.70  
  Purchase #5 $146.82   6.821%   $156.8346   $156.83   $156.85   $156.80  
  Purchase #6 $135.49   11.606%   $151.215   $151.22   $151.20   $151.20  
  Purchase #7 $19.87   8.530%   $21.5649   $21.56   $21.55   $21.60  
  7 purchase totals = $620.59       $682.0327   $682.03   $682.00   $682.00