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 $56.90   12.398%   $63.9545   $63.95   $63.95   $64.00  
  Purchase #2 $32.42   5.202%   $34.1065   $34.11   $34.10   $34.10  
  Purchase #3 $19.47   8.858%   $21.1947   $21.19   $21.20   $21.20  
  Purchase #4 $88.75   11.213%   $98.7015   $98.70   $98.70   $98.70  
  Purchase #5 $98.76   13.379%   $111.9731   $111.97   $111.95   $112.00  
  Purchase #6 $17.56   5.498%   $18.5254   $18.53   $18.55   $18.50  
  Purchase #7 $72.77   9.669%   $79.8061   $79.81   $79.80   $79.80  
  7 purchase totals = $386.63       $428.2618   $428.26   $428.25   $428.30