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 $110.90   13.626%   $126.0112   $126.01   $126.00   $126.00  
  Purchase #2 $238.68   4.392%   $249.1628   $249.16   $249.15   $249.20  
  Purchase #3 $65.99   6.691%   $70.4054   $70.41   $70.40   $70.40  
  Purchase #4 $111.40   13.859%   $126.8389   $126.84   $126.85   $126.80  
  Purchase #5 $161.94   12.650%   $182.4254   $182.43   $182.45   $182.40  
  Purchase #6 $131.72   11.333%   $146.6478   $146.65   $146.65   $146.60  
  Purchase #7 $114.74   7.156%   $122.9508   $122.95   $122.95   $123.00  
  7 purchase totals = $935.37       $1,024.4423   $1,024.45   $1,024.45   $1,024.40