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 $59.31   4.358%   $61.8947   $61.89   $61.90   $61.90  
  Purchase #2 $138.25   13.244%   $156.5598   $156.56   $156.55   $156.60  
  Purchase #3 $183.71   9.725%   $201.5758   $201.58   $201.60   $201.60  
  Purchase #4 $240.90   4.709%   $252.244   $252.24   $252.25   $252.20  
  Purchase #5 $59.76   4.246%   $62.2974   $62.30   $62.30   $62.30  
  Purchase #6 $136.78   6.529%   $145.7104   $145.71   $145.70   $145.70  
  Purchase #7 $101.32   12.707%   $114.1947   $114.19   $114.20   $114.20  
  7 purchase totals = $920.03       $994.4768   $994.47   $994.50   $994.50