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 $211.31   13.841%   $240.5574   $240.56   $240.55   $240.60  
  Purchase #2 $17.26   6.796%   $18.433   $18.43   $18.45   $18.40  
  Purchase #3 $228.42   6.139%   $242.4427   $242.44   $242.45   $242.40  
  Purchase #4 $179.42   13.637%   $203.8875   $203.89   $203.90   $203.90  
  Purchase #5 $131.56   3.175%   $135.737   $135.74   $135.75   $135.70  
  Purchase #6 $239.40   4.625%   $250.4723   $250.47   $250.45   $250.50  
  Purchase #7 $25.76   8.447%   $27.9359   $27.94   $27.95   $27.90  
  7 purchase totals = $1,033.13       $1,119.4658   $1,119.47   $1,119.50   $1,119.40