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 $76.97   11.702%   $85.977   $85.98   $86.00   $86.00  
  Purchase #2 $228.93   4.673%   $239.6279   $239.63   $239.65   $239.60  
  Purchase #3 $52.36   8.752%   $56.9425   $56.94   $56.95   $56.90  
  Purchase #4 $113.91   8.518%   $123.6129   $123.61   $123.60   $123.60  
  Purchase #5 $96.61   12.459%   $108.6466   $108.65   $108.65   $108.60  
  Purchase #6 $54.69   3.510%   $56.6096   $56.61   $56.60   $56.60  
  Purchase #7 $172.73   4.322%   $180.1954   $180.20   $180.20   $180.20  
  7 purchase totals = $796.20       $851.6119   $851.62   $851.65   $851.50