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 $91.40   6.760%   $97.5786   $97.58   $97.60   $97.60  
  Purchase #2 $120.34   5.209%   $126.6085   $126.61   $126.60   $126.60  
  Purchase #3 $104.73   8.863%   $114.0122   $114.01   $114.00   $114.00  
  Purchase #4 $201.47   6.608%   $214.7831   $214.78   $214.80   $214.80  
  Purchase #5 $16.74   3.630%   $17.3477   $17.35   $17.35   $17.30  
  Purchase #6 $118.61   9.311%   $129.6538   $129.65   $129.65   $129.70  
  Purchase #7 $157.55   12.200%   $176.7711   $176.77   $176.75   $176.80  
  7 purchase totals = $810.84       $876.7550   $876.75   $876.75   $876.80