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 $213.33   12.154%   $239.2581   $239.26   $239.25   $239.30  
  Purchase #2 $61.75   9.397%   $67.5526   $67.55   $67.55   $67.60  
  Purchase #3 $98.85   13.767%   $112.4587   $112.46   $112.45   $112.50  
  Purchase #4 $92.36   6.536%   $98.3966   $98.40   $98.40   $98.40  
  Purchase #5 $50.95   4.870%   $53.4313   $53.43   $53.45   $53.40  
  Purchase #6 $165.27   5.685%   $174.6656   $174.67   $174.65   $174.70  
  Purchase #7 $98.86   8.373%   $107.1375   $107.14   $107.15   $107.10  
  7 purchase totals = $781.37       $852.9004   $852.91   $852.90   $853.00