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 $72.93   5.353%   $76.8339   $76.83   $76.85   $76.80  
  Purchase #2 $150.26   10.228%   $165.6286   $165.63   $165.65   $165.60  
  Purchase #3 $121.46   11.493%   $135.4194   $135.42   $135.40   $135.40  
  Purchase #4 $201.53   5.437%   $212.4872   $212.49   $212.50   $212.50  
  Purchase #5 $77.41   10.856%   $85.8136   $85.81   $85.80   $85.80  
  Purchase #6 $22.31   3.477%   $23.0857   $23.09   $23.10   $23.10  
  Purchase #7 $164.66   11.376%   $183.3917   $183.39   $183.40   $183.40  
  7 purchase totals = $810.56       $882.6601   $882.66   $882.70   $882.60