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 $209.85   11.846%   $234.7088   $234.71   $234.70   $234.70  
  Purchase #2 $176.32   9.659%   $193.3507   $193.35   $193.35   $193.40  
  Purchase #3 $73.36   11.523%   $81.8133   $81.81   $81.80   $81.80  
  Purchase #4 $225.77   3.685%   $234.0896   $234.09   $234.10   $234.10  
  Purchase #5 $140.73   12.437%   $158.2326   $158.23   $158.25   $158.20  
  Purchase #6 $112.97   10.485%   $124.8149   $124.81   $124.80   $124.80  
  Purchase #7 $105.74   8.379%   $114.6   $114.60   $114.60   $114.60  
  7 purchase totals = $1,044.74       $1,141.6099   $1,141.60   $1,141.60   $1,141.60