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 $241.49   8.433%   $261.8549   $261.85   $261.85   $261.90  
  Purchase #2 $119.46   6.694%   $127.4567   $127.46   $127.45   $127.50  
  Purchase #3 $52.54   9.842%   $57.711   $57.71   $57.70   $57.70  
  Purchase #4 $245.48   11.232%   $273.0523   $273.05   $273.05   $273.10  
  Purchase #5 $35.42   7.284%   $38   $38.00   $38.00   $38.00  
  Purchase #6 $24.48   6.593%   $26.094   $26.09   $26.10   $26.10  
  Purchase #7 $93.54   6.631%   $99.7426   $99.74   $99.75   $99.70  
  7 purchase totals = $812.41       $883.9115   $883.90   $883.90   $884.00