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 $23.85   10.697%   $26.4012   $26.40   $26.40   $26.40  
  Purchase #2 $54.42   4.543%   $56.8923   $56.89   $56.90   $56.90  
  Purchase #3 $185.64   6.799%   $198.2617   $198.26   $198.25   $198.30  
  Purchase #4 $68.55   13.293%   $77.6624   $77.66   $77.65   $77.70  
  Purchase #5 $174.52   10.806%   $193.3786   $193.38   $193.40   $193.40  
  Purchase #6 $210.39   3.604%   $217.9725   $217.97   $217.95   $218.00  
  Purchase #7 $173.60   13.144%   $196.418   $196.42   $196.40   $196.40  
  7 purchase totals = $890.97       $966.9867   $966.98   $966.95   $967.10