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 $217.61   10.557%   $240.5831   $240.58   $240.60   $240.60  
  Purchase #2 $92.92   9.423%   $101.6759   $101.68   $101.70   $101.70  
  Purchase #3 $93.34   5.111%   $98.1106   $98.11   $98.10   $98.10  
  Purchase #4 $222.89   12.724%   $251.2505   $251.25   $251.25   $251.30  
  Purchase #5 $64.99   9.318%   $71.0458   $71.05   $71.05   $71.00  
  Purchase #6 $246.39   10.721%   $272.8055   $272.81   $272.80   $272.80  
  Purchase #7 $113.25   12.195%   $127.0608   $127.06   $127.05   $127.10  
  7 purchase totals = $1,051.39       $1,162.5322   $1,162.54   $1,162.55   $1,162.60