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 $227.98   13.681%   $259.1699   $259.17   $259.15   $259.20  
  Purchase #2 $114.75   3.844%   $119.161   $119.16   $119.15   $119.20  
  Purchase #3 $115.46   3.388%   $119.3718   $119.37   $119.35   $119.40  
  Purchase #4 $207.98   13.474%   $236.0032   $236.00   $236.00   $236.00  
  Purchase #5 $110.35   13.179%   $124.893   $124.89   $124.90   $124.90  
  Purchase #6 $74.72   5.688%   $78.9701   $78.97   $78.95   $79.00  
  Purchase #7 $27.40   7.177%   $29.3665   $29.37   $29.35   $29.40  
  7 purchase totals = $878.64       $966.9355   $966.93   $966.85   $967.10