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 $241.54   8.697%   $262.5467   $262.55   $262.55   $262.50  
  Purchase #2 $241.72   6.738%   $258.0071   $258.01   $258.00   $258.00  
  Purchase #3 $87.62   8.456%   $95.0291   $95.03   $95.05   $95.00  
  Purchase #4 $63.52   3.105%   $65.4923   $65.49   $65.50   $65.50  
  Purchase #5 $98.42   6.555%   $104.8714   $104.87   $104.85   $104.90  
  Purchase #6 $21.66   3.641%   $22.4486   $22.45   $22.45   $22.40  
  Purchase #7 $24.99   4.706%   $26.166   $26.17   $26.15   $26.20  
  7 purchase totals = $779.47       $834.5612   $834.57   $834.55   $834.50