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 $52.72   13.430%   $59.8003   $59.80   $59.80   $59.80  
  Purchase #2 $123.90   9.824%   $136.0719   $136.07   $136.05   $136.10  
  Purchase #3 $182.36   6.200%   $193.6663   $193.67   $193.65   $193.70  
  Purchase #4 $241.62   8.428%   $261.9837   $261.98   $262.00   $262.00  
  Purchase #5 $40.49   12.735%   $45.6464   $45.65   $45.65   $45.60  
  Purchase #6 $114.89   13.493%   $130.3921   $130.39   $130.40   $130.40  
  Purchase #7 $248.65   3.837%   $258.1907   $258.19   $258.20   $258.20  
  7 purchase totals = $1,004.63       $1,085.7514   $1,085.75   $1,085.75   $1,085.80