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 $247.94   5.655%   $261.961   $261.96   $261.95   $262.00  
  Purchase #2 $24.99   3.524%   $25.8706   $25.87   $25.85   $25.90  
  Purchase #3 $228.54   9.510%   $250.2742   $250.27   $250.25   $250.30  
  Purchase #4 $15.42   3.417%   $15.9469   $15.95   $15.95   $15.90  
  Purchase #5 $66.69   13.311%   $75.5671   $75.57   $75.55   $75.60  
  Purchase #6 $155.35   13.853%   $176.8706   $176.87   $176.85   $176.90  
  Purchase #7 $40.44   9.147%   $44.139   $44.14   $44.15   $44.10  
  7 purchase totals = $779.37       $850.6294   $850.63   $850.55   $850.70