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 $86.60   12.756%   $97.6467   $97.65   $97.65   $97.60  
  Purchase #2 $173.75   7.868%   $187.4207   $187.42   $187.40   $187.40  
  Purchase #3 $222.63   12.554%   $250.579   $250.58   $250.60   $250.60  
  Purchase #4 $35.35   3.493%   $36.5848   $36.58   $36.60   $36.60  
  Purchase #5 $186.75   10.247%   $205.8863   $205.89   $205.90   $205.90  
  Purchase #6 $175.71   12.393%   $197.4857   $197.49   $197.50   $197.50  
  Purchase #7 $96.88   13.778%   $110.2281   $110.23   $110.25   $110.20  
  7 purchase totals = $977.67       $1,085.8313   $1,085.84   $1,085.90   $1,085.80