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 $167.79   3.849%   $174.2482   $174.25   $174.25   $174.20  
  Purchase #2 $71.88   10.398%   $79.3541   $79.35   $79.35   $79.40  
  Purchase #3 $24.83   7.197%   $26.617   $26.62   $26.60   $26.60  
  Purchase #4 $85.94   11.579%   $95.891   $95.89   $95.90   $95.90  
  Purchase #5 $248.35   8.197%   $268.7072   $268.71   $268.70   $268.70  
  Purchase #6 $13.78   4.393%   $14.3854   $14.39   $14.40   $14.40  
  Purchase #7 $244.87   13.234%   $277.2761   $277.28   $277.30   $277.30  
  7 purchase totals = $857.44       $936.4790   $936.49   $936.50   $936.50