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 $198.87   8.451%   $215.6765   $215.68   $215.70   $215.70  
  Purchase #2 $63.28   3.761%   $65.66   $65.66   $65.65   $65.70  
  Purchase #3 $56.77   3.165%   $58.5668   $58.57   $58.55   $58.60  
  Purchase #4 $69.75   8.807%   $75.8929   $75.89   $75.90   $75.90  
  Purchase #5 $102.88   13.819%   $117.097   $117.10   $117.10   $117.10  
  Purchase #6 $44.63   7.348%   $47.9094   $47.91   $47.90   $47.90  
  Purchase #7 $249.93   10.250%   $275.5478   $275.55   $275.55   $275.50  
  7 purchase totals = $786.11       $856.3504   $856.36   $856.35   $856.40