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 $206.48   12.725%   $232.7546   $232.75   $232.75   $232.80  
  Purchase #2 $130.54   7.713%   $140.6086   $140.61   $140.60   $140.60  
  Purchase #3 $11.45   6.832%   $12.2323   $12.23   $12.25   $12.20  
  Purchase #4 $190.63   12.298%   $214.0737   $214.07   $214.05   $214.10  
  Purchase #5 $44.43   3.705%   $46.0761   $46.08   $46.10   $46.10  
  Purchase #6 $67.34   4.256%   $70.206   $70.21   $70.20   $70.20  
  Purchase #7 $236.30   12.609%   $266.0951   $266.10   $266.10   $266.10  
  7 purchase totals = $887.17       $982.0464   $982.05   $982.05   $982.10