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 $248.76   5.336%   $262.0338   $262.03   $262.05   $262.00  
  Purchase #2 $94.63   9.830%   $103.9321   $103.93   $103.95   $103.90  
  Purchase #3 $43.75   5.587%   $46.1943   $46.19   $46.20   $46.20  
  Purchase #4 $226.30   3.677%   $234.6211   $234.62   $234.60   $234.60  
  Purchase #5 $61.88   6.615%   $65.9734   $65.97   $65.95   $66.00  
  Purchase #6 $174.54   13.863%   $198.7365   $198.74   $198.75   $198.70  
  Purchase #7 $16.46   10.263%   $18.1493   $18.15   $18.15   $18.10  
  7 purchase totals = $866.32       $929.6405   $929.63   $929.65   $929.50