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 $50.46   12.252%   $56.6424   $56.64   $56.65   $56.60  
  Purchase #2 $55.62   11.455%   $61.9913   $61.99   $62.00   $62.00  
  Purchase #3 $162.61   8.225%   $175.9847   $175.98   $176.00   $176.00  
  Purchase #4 $26.67   12.235%   $29.9331   $29.93   $29.95   $29.90  
  Purchase #5 $61.32   8.843%   $66.7425   $66.74   $66.75   $66.70  
  Purchase #6 $145.84   9.328%   $159.444   $159.44   $159.45   $159.40  
  Purchase #7 $221.81   12.116%   $248.6845   $248.68   $248.70   $248.70  
  7 purchase totals = $724.33       $799.4225   $799.40   $799.50   $799.30