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 $87.88   9.719%   $96.4211   $96.42   $96.40   $96.40  
  Purchase #2 $230.48   13.739%   $262.1456   $262.15   $262.15   $262.10  
  Purchase #3 $9.30   7.715%   $10.0175   $10.02   $10.00   $10.00  
  Purchase #4 $195.69   9.138%   $213.5722   $213.57   $213.55   $213.60  
  Purchase #5 $61.75   11.249%   $68.6963   $68.70   $68.70   $68.70  
  Purchase #6 $60.69   8.724%   $65.9846   $65.98   $66.00   $66.00  
  Purchase #7 $63.99   9.268%   $69.9206   $69.92   $69.90   $69.90  
  7 purchase totals = $709.78       $786.7579   $786.76   $786.70   $786.70