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 $101.54   12.460%   $114.1919   $114.19   $114.20   $114.20  
  Purchase #2 $131.42   4.870%   $137.8202   $137.82   $137.80   $137.80  
  Purchase #3 $105.90   6.761%   $113.0599   $113.06   $113.05   $113.10  
  Purchase #4 $42.54   9.780%   $46.7004   $46.70   $46.70   $46.70  
  Purchase #5 $183.89   12.635%   $207.1245   $207.12   $207.10   $207.10  
  Purchase #6 $127.61   6.809%   $136.299   $136.30   $136.30   $136.30  
  Purchase #7 $16.53   11.572%   $18.4429   $18.44   $18.45   $18.40  
  7 purchase totals = $709.43       $773.6388   $773.63   $773.60   $773.60