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 $208.32   13.724%   $236.9098   $236.91   $236.90   $236.90  
  Purchase #2 $24.30   3.438%   $25.1354   $25.14   $25.15   $25.10  
  Purchase #3 $89.36   3.272%   $92.2839   $92.28   $92.30   $92.30  
  Purchase #4 $90.68   4.724%   $94.9637   $94.96   $94.95   $95.00  
  Purchase #5 $104.71   13.217%   $118.5495   $118.55   $118.55   $118.50  
  Purchase #6 $170.44   5.557%   $179.9114   $179.91   $179.90   $179.90  
  Purchase #7 $204.41   8.617%   $222.024   $222.02   $222.00   $222.00  
  7 purchase totals = $892.22       $969.7777   $969.77   $969.75   $969.70