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 $183.63   13.783%   $208.9397   $208.94   $208.95   $208.90  
  Purchase #2 $33.83   5.322%   $35.6304   $35.63   $35.65   $35.60  
  Purchase #3 $90.42   8.323%   $97.9457   $97.95   $97.95   $97.90  
  Purchase #4 $226.69   11.853%   $253.5596   $253.56   $253.55   $253.60  
  Purchase #5 $148.97   3.733%   $154.5311   $154.53   $154.55   $154.50  
  Purchase #6 $168.72   10.798%   $186.9384   $186.94   $186.95   $186.90  
  Purchase #7 $184.70   8.340%   $200.104   $200.10   $200.10   $200.10  
  7 purchase totals = $1,036.96       $1,137.6489   $1,137.65   $1,137.70   $1,137.50