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 $25.34   4.578%   $26.5001   $26.50   $26.50   $26.50  
  Purchase #2 $227.34   13.572%   $258.1946   $258.19   $258.20   $258.20  
  Purchase #3 $60.94   9.421%   $66.6812   $66.68   $66.70   $66.70  
  Purchase #4 $238.71   7.302%   $256.1406   $256.14   $256.15   $256.10  
  Purchase #5 $170.50   13.232%   $193.0606   $193.06   $193.05   $193.10  
  Purchase #6 $173.45   8.870%   $188.835   $188.84   $188.85   $188.80  
  Purchase #7 $71.55   9.573%   $78.3995   $78.40   $78.40   $78.40  
  7 purchase totals = $967.83       $1,067.8116   $1,067.81   $1,067.85   $1,067.80