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 $67.27   3.753%   $69.7946   $69.79   $69.80   $69.80  
  Purchase #2 $127.89   10.273%   $141.0281   $141.03   $141.05   $141.00  
  Purchase #3 $216.45   5.149%   $227.595   $227.60   $227.60   $227.60  
  Purchase #4 $17.61   6.461%   $18.7478   $18.75   $18.75   $18.70  
  Purchase #5 $203.89   3.340%   $210.6999   $210.70   $210.70   $210.70  
  Purchase #6 $52.59   8.509%   $57.0649   $57.06   $57.05   $57.10  
  Purchase #7 $68.63   13.247%   $77.7214   $77.72   $77.70   $77.70  
  7 purchase totals = $754.33       $802.6517   $802.65   $802.65   $802.60