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 $57.32   10.282%   $63.2136   $63.21   $63.20   $63.20  
  Purchase #2 $95.41   8.724%   $103.7336   $103.73   $103.75   $103.70  
  Purchase #3 $219.83   9.727%   $241.2129   $241.21   $241.20   $241.20  
  Purchase #4 $15.57   8.545%   $16.9005   $16.90   $16.90   $16.90  
  Purchase #5 $56.46   5.605%   $59.6246   $59.62   $59.60   $59.60  
  Purchase #6 $63.48   13.706%   $72.1806   $72.18   $72.20   $72.20  
  Purchase #7 $188.49   10.467%   $208.2192   $208.22   $208.20   $208.20  
  7 purchase totals = $696.56       $765.0850   $765.07   $765.05   $765.00