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 $23.31   12.453%   $26.2128   $26.21   $26.20   $26.20  
  Purchase #2 $46.41   7.571%   $49.9237   $49.92   $49.90   $49.90  
  Purchase #3 $38.68   12.727%   $43.6028   $43.60   $43.60   $43.60  
  Purchase #4 $211.38   5.773%   $223.583   $223.58   $223.60   $223.60  
  Purchase #5 $124.77   7.807%   $134.5108   $134.51   $134.50   $134.50  
  Purchase #6 $68.61   11.721%   $76.6518   $76.65   $76.65   $76.70  
  Purchase #7 $153.79   12.750%   $173.3982   $173.40   $173.40   $173.40  
  7 purchase totals = $666.95       $727.8831   $727.87   $727.85   $727.90