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 $44.95   12.196%   $50.4321   $50.43   $50.45   $50.40  
  Purchase #2 $108.35   13.181%   $122.6316   $122.63   $122.65   $122.60  
  Purchase #3 $54.81   13.117%   $61.9994   $62.00   $62.00   $62.00  
  Purchase #4 $104.36   6.622%   $111.2707   $111.27   $111.25   $111.30  
  Purchase #5 $192.95   7.820%   $208.0387   $208.04   $208.05   $208.00  
  Purchase #6 $229.39   9.336%   $250.8059   $250.81   $250.80   $250.80  
  Purchase #7 $192.58   3.724%   $199.7517   $199.75   $199.75   $199.80  
  7 purchase totals = $927.39       $1,004.9301   $1,004.93   $1,004.95   $1,004.90