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 $248.41   4.871%   $260.5101   $260.51   $260.50   $260.50  
  Purchase #2 $250.25   3.411%   $258.786   $258.79   $258.80   $258.80  
  Purchase #3 $54.44   13.725%   $61.9119   $61.91   $61.90   $61.90  
  Purchase #4 $83.59   10.822%   $92.6361   $92.64   $92.65   $92.60  
  Purchase #5 $60.81   13.867%   $69.2425   $69.24   $69.25   $69.20  
  Purchase #6 $215.70   8.833%   $234.7528   $234.75   $234.75   $234.80  
  Purchase #7 $245.79   8.395%   $266.4241   $266.42   $266.40   $266.40  
  7 purchase totals = $1,158.99       $1,244.2635   $1,244.26   $1,244.25   $1,244.20