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 $210.99   13.280%   $239.0095   $239.01   $239.00   $239.00  
  Purchase #2 $34.63   3.122%   $35.7111   $35.71   $35.70   $35.70  
  Purchase #3 $111.35   5.108%   $117.0378   $117.04   $117.05   $117.00  
  Purchase #4 $80.96   6.227%   $86.0014   $86.00   $86.00   $86.00  
  Purchase #5 $208.37   13.624%   $236.7583   $236.76   $236.75   $236.80  
  Purchase #6 $56.45   12.423%   $63.4628   $63.46   $63.45   $63.50  
  Purchase #7 $226.51   13.793%   $257.7525   $257.75   $257.75   $257.80  
  7 purchase totals = $929.26       $1,035.7334   $1,035.73   $1,035.70   $1,035.80