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 $87.62   5.715%   $92.6275   $92.63   $92.65   $92.60  
  Purchase #2 $190.94   5.264%   $200.9911   $200.99   $201.00   $201.00  
  Purchase #3 $89.66   11.867%   $100.3   $100.30   $100.30   $100.30  
  Purchase #4 $143.46   3.806%   $148.9201   $148.92   $148.90   $148.90  
  Purchase #5 $76.82   6.788%   $82.0345   $82.03   $82.05   $82.00  
  Purchase #6 $29.36   12.704%   $33.0899   $33.09   $33.10   $33.10  
  Purchase #7 $226.81   6.218%   $240.913   $240.91   $240.90   $240.90  
  7 purchase totals = $844.67       $898.8761   $898.87   $898.90   $898.80