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 $78.62   8.655%   $85.4246   $85.42   $85.40   $85.40  
  Purchase #2 $247.94   7.604%   $266.7934   $266.79   $266.80   $266.80  
  Purchase #3 $11.76   8.692%   $12.7822   $12.78   $12.80   $12.80  
  Purchase #4 $195.66   11.358%   $217.8831   $217.88   $217.90   $217.90  
  Purchase #5 $50.77   11.285%   $56.4994   $56.50   $56.50   $56.50  
  Purchase #6 $74.29   10.701%   $82.2398   $82.24   $82.25   $82.20  
  Purchase #7 $36.28   7.577%   $39.0289   $39.03   $39.05   $39.00  
  7 purchase totals = $695.32       $760.6514   $760.64   $760.70   $760.60