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 $208.82   8.267%   $226.0831   $226.08   $226.10   $226.10  
  Purchase #2 $212.46   9.264%   $232.1423   $232.14   $232.15   $232.10  
  Purchase #3 $166.54   3.762%   $172.8052   $172.81   $172.80   $172.80  
  Purchase #4 $238.38   9.522%   $261.0785   $261.08   $261.10   $261.10  
  Purchase #5 $56.30   13.682%   $64.003   $64.00   $64.00   $64.00  
  Purchase #6 $238.37   10.845%   $264.2212   $264.22   $264.20   $264.20  
  Purchase #7 $201.44   13.484%   $228.6022   $228.60   $228.60   $228.60  
  7 purchase totals = $1,322.31       $1,448.9355   $1,448.93   $1,448.95   $1,448.90