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 $68.30   12.601%   $76.9065   $76.91   $76.90   $76.90  
  Purchase #2 $150.83   10.528%   $166.7094   $166.71   $166.70   $166.70  
  Purchase #3 $146.28   7.836%   $157.7425   $157.74   $157.75   $157.70  
  Purchase #4 $177.63   13.189%   $201.0576   $201.06   $201.05   $201.10  
  Purchase #5 $188.97   10.356%   $208.5397   $208.54   $208.55   $208.50  
  Purchase #6 $199.42   8.153%   $215.6787   $215.68   $215.70   $215.70  
  Purchase #7 $159.76   10.194%   $176.0459   $176.05   $176.05   $176.00  
  7 purchase totals = $1,091.19       $1,202.6803   $1,202.69   $1,202.70   $1,202.60