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 $214.85   12.595%   $241.9104   $241.91   $241.90   $241.90  
  Purchase #2 $230.63   11.223%   $256.5136   $256.51   $256.50   $256.50  
  Purchase #3 $21.32   12.544%   $23.9944   $23.99   $24.00   $24.00  
  Purchase #4 $75.26   13.622%   $85.5119   $85.51   $85.50   $85.50  
  Purchase #5 $26.51   7.242%   $28.4299   $28.43   $28.45   $28.40  
  Purchase #6 $57.68   9.331%   $63.0621   $63.06   $63.05   $63.10  
  Purchase #7 $197.51   13.773%   $224.7131   $224.71   $224.70   $224.70  
  7 purchase totals = $823.76       $924.1354   $924.12   $924.10   $924.10