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 $78.46   10.532%   $86.7234   $86.72   $86.70   $86.70  
  Purchase #2 $80.66   3.273%   $83.3   $83.30   $83.30   $83.30  
  Purchase #3 $123.81   3.854%   $128.5816   $128.58   $128.60   $128.60  
  Purchase #4 $154.82   5.586%   $163.4682   $163.47   $163.45   $163.50  
  Purchase #5 $122.46   3.271%   $126.4657   $126.47   $126.45   $126.50  
  Purchase #6 $41.60   12.838%   $46.9406   $46.94   $46.95   $46.90  
  Purchase #7 $124.61   7.738%   $134.2523   $134.25   $134.25   $134.30  
  7 purchase totals = $726.42       $769.7318   $769.73   $769.70   $769.80