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 $161.65   9.549%   $177.086   $177.09   $177.10   $177.10  
  Purchase #2 $224.32   11.468%   $250.045   $250.05   $250.05   $250.00  
  Purchase #3 $65.33   13.109%   $73.8941   $73.89   $73.90   $73.90  
  Purchase #4 $72.79   5.483%   $76.7811   $76.78   $76.80   $76.80  
  Purchase #5 $133.43   8.635%   $144.9517   $144.95   $144.95   $145.00  
  Purchase #6 $63.65   10.557%   $70.3695   $70.37   $70.35   $70.40  
  Purchase #7 $212.99   13.661%   $242.0866   $242.09   $242.10   $242.10  
  7 purchase totals = $934.16       $1,035.2140   $1,035.22   $1,035.25   $1,035.30