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 $239.74   11.720%   $267.8375   $267.84   $267.85   $267.80  
  Purchase #2 $190.26   10.874%   $210.9489   $210.95   $210.95   $210.90  
  Purchase #3 $220.60   12.697%   $248.6096   $248.61   $248.60   $248.60  
  Purchase #4 $163.77   8.122%   $177.0714   $177.07   $177.05   $177.10  
  Purchase #5 $25.26   8.760%   $27.4728   $27.47   $27.45   $27.50  
  Purchase #6 $42.48   10.115%   $46.7769   $46.78   $46.80   $46.80  
  Purchase #7 $249.66   6.743%   $266.4946   $266.49   $266.50   $266.50  
  7 purchase totals = $1,131.77       $1,245.2117   $1,245.21   $1,245.20   $1,245.20