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 $104.97   9.511%   $114.9537   $114.95   $114.95   $115.00  
  Purchase #2 $240.45   10.543%   $265.8006   $265.80   $265.80   $265.80  
  Purchase #3 $73.80   12.108%   $82.7357   $82.74   $82.75   $82.70  
  Purchase #4 $11.68   6.380%   $12.4252   $12.43   $12.45   $12.40  
  Purchase #5 $56.55   11.459%   $63.0301   $63.03   $63.05   $63.00  
  Purchase #6 $243.54   4.750%   $255.1082   $255.11   $255.10   $255.10  
  Purchase #7 $34.46   3.408%   $35.6344   $35.63   $35.65   $35.60  
  7 purchase totals = $765.45       $829.6879   $829.69   $829.75   $829.60