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 $240.93   11.663%   $269.0297   $269.03   $269.05   $269.00  
  Purchase #2 $26.86   12.677%   $30.265   $30.27   $30.25   $30.30  
  Purchase #3 $71.58   7.724%   $77.1088   $77.11   $77.10   $77.10  
  Purchase #4 $94.89   12.393%   $106.6497   $106.65   $106.65   $106.60  
  Purchase #5 $72.44   9.143%   $79.0632   $79.06   $79.05   $79.10  
  Purchase #6 $64.65   8.277%   $70.0011   $70.00   $70.00   $70.00  
  Purchase #7 $134.96   13.321%   $152.938   $152.94   $152.95   $152.90  
  7 purchase totals = $706.31       $785.0555   $785.06   $785.05   $785.00