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 $190.87   12.139%   $214.0397   $214.04   $214.05   $214.00  
  Purchase #2 $162.92   10.673%   $180.3085   $180.31   $180.30   $180.30  
  Purchase #3 $126.93   12.238%   $142.4637   $142.46   $142.45   $142.50  
  Purchase #4 $50.35   13.116%   $56.9539   $56.95   $56.95   $57.00  
  Purchase #5 $69.90   4.853%   $73.2922   $73.29   $73.30   $73.30  
  Purchase #6 $213.38   3.438%   $220.716   $220.72   $220.70   $220.70  
  Purchase #7 $115.84   7.162%   $124.1365   $124.14   $124.15   $124.10  
  7 purchase totals = $930.19       $1,011.9105   $1,011.91   $1,011.90   $1,011.90