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 $23.64   11.141%   $26.2737   $26.27   $26.25   $26.30  
  Purchase #2 $225.64   10.787%   $249.9798   $249.98   $250.00   $250.00  
  Purchase #3 $56.43   9.708%   $61.9082   $61.91   $61.90   $61.90  
  Purchase #4 $83.36   4.633%   $87.2221   $87.22   $87.20   $87.20  
  Purchase #5 $19.32   11.256%   $21.4947   $21.49   $21.50   $21.50  
  Purchase #6 $12.78   12.611%   $14.3917   $14.39   $14.40   $14.40  
  Purchase #7 $235.37   11.499%   $262.4352   $262.44   $262.45   $262.40  
  7 purchase totals = $656.54       $723.7054   $723.70   $723.70   $723.70