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 $197.81   5.220%   $208.1357   $208.14   $208.15   $208.10  
  Purchase #2 $6.49   6.794%   $6.9309   $6.93   $6.95   $6.90  
  Purchase #3 $95.74   7.566%   $102.9837   $102.98   $103.00   $103.00  
  Purchase #4 $10.89   4.811%   $11.4139   $11.41   $11.40   $11.40  
  Purchase #5 $193.85   10.671%   $214.5357   $214.54   $214.55   $214.50  
  Purchase #6 $169.49   7.538%   $182.2662   $182.27   $182.25   $182.30  
  Purchase #7 $56.87   10.218%   $62.681   $62.68   $62.70   $62.70  
  7 purchase totals = $731.14       $788.9471   $788.95   $789.00   $788.90