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 $57.58   9.609%   $63.1129   $63.11   $63.10   $63.10  
  Purchase #2 $234.91   5.773%   $248.4714   $248.47   $248.45   $248.50  
  Purchase #3 $187.78   4.454%   $196.1437   $196.14   $196.15   $196.10  
  Purchase #4 $46.77   11.861%   $52.3174   $52.32   $52.30   $52.30  
  Purchase #5 $236.58   13.153%   $267.6974   $267.70   $267.70   $267.70  
  Purchase #6 $214.68   3.368%   $221.9104   $221.91   $221.90   $221.90  
  Purchase #7 $7.86   13.578%   $8.9272   $8.93   $8.95   $8.90  
  7 purchase totals = $986.16       $1,058.5804   $1,058.58   $1,058.55   $1,058.50