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 $179.43   6.399%   $190.9117   $190.91   $190.90   $190.90  
  Purchase #2 $116.61   11.604%   $130.1414   $130.14   $130.15   $130.10  
  Purchase #3 $29.54   4.314%   $30.8144   $30.81   $30.80   $30.80  
  Purchase #4 $105.36   11.175%   $117.134   $117.13   $117.15   $117.10  
  Purchase #5 $106.70   7.285%   $114.4731   $114.47   $114.45   $114.50  
  Purchase #6 $176.40   13.291%   $199.8453   $199.85   $199.85   $199.80  
  Purchase #7 $77.35   8.716%   $84.0918   $84.09   $84.10   $84.10  
  7 purchase totals = $791.39       $867.4117   $867.40   $867.40   $867.30