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 $136.81   10.373%   $151.0013   $151.00   $151.00   $151.00  
  Purchase #2 $176.89   11.724%   $197.6286   $197.63   $197.65   $197.60  
  Purchase #3 $38.31   12.429%   $43.0715   $43.07   $43.05   $43.10  
  Purchase #4 $106.95   6.673%   $114.0868   $114.09   $114.10   $114.10  
  Purchase #5 $153.63   6.247%   $163.2273   $163.23   $163.25   $163.20  
  Purchase #6 $223.47   8.347%   $242.123   $242.12   $242.10   $242.10  
  Purchase #7 $80.31   5.328%   $84.5889   $84.59   $84.60   $84.60  
  7 purchase totals = $916.37       $995.7274   $995.73   $995.75   $995.70