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 $107.68   10.737%   $119.2416   $119.24   $119.25   $119.20  
  Purchase #2 $245.42   5.137%   $258.0272   $258.03   $258.05   $258.00  
  Purchase #3 $65.77   6.423%   $69.9944   $69.99   $70.00   $70.00  
  Purchase #4 $76.94   11.260%   $85.6034   $85.60   $85.60   $85.60  
  Purchase #5 $75.72   7.132%   $81.1204   $81.12   $81.10   $81.10  
  Purchase #6 $226.73   11.870%   $253.6429   $253.64   $253.65   $253.60  
  Purchase #7 $28.69   7.463%   $30.8311   $30.83   $30.85   $30.80  
  7 purchase totals = $826.95       $898.4610   $898.45   $898.50   $898.30