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 $232.25   11.797%   $259.6485   $259.65   $259.65   $259.60  
  Purchase #2 $182.45   8.522%   $197.9984   $198.00   $198.00   $198.00  
  Purchase #3 $143.44   8.724%   $155.9537   $155.95   $155.95   $156.00  
  Purchase #4 $183.74   3.546%   $190.2554   $190.26   $190.25   $190.30  
  Purchase #5 $85.90   11.438%   $95.7252   $95.73   $95.75   $95.70  
  Purchase #6 $180.98   4.291%   $188.7459   $188.75   $188.75   $188.70  
  Purchase #7 $155.72   13.427%   $176.6285   $176.63   $176.65   $176.60  
  7 purchase totals = $1,164.48       $1,264.9556   $1,264.97   $1,265.00   $1,264.90