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 $137.75   13.685%   $156.6011   $156.60   $156.60   $156.60  
  Purchase #2 $196.88   7.202%   $211.0593   $211.06   $211.05   $211.10  
  Purchase #3 $66.25   10.567%   $73.2506   $73.25   $73.25   $73.30  
  Purchase #4 $175.63   8.814%   $191.11   $191.11   $191.10   $191.10  
  Purchase #5 $236.46   4.706%   $247.5878   $247.59   $247.60   $247.60  
  Purchase #6 $199.65   4.678%   $208.9896   $208.99   $209.00   $209.00  
  Purchase #7 $8.42   6.857%   $8.9974   $9.00   $9.00   $9.00  
  7 purchase totals = $1,021.04       $1,097.5958   $1,097.60   $1,097.60   $1,097.70