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 $113.57   5.373%   $119.6721   $119.67   $119.65   $119.70  
  Purchase #2 $250.34   9.305%   $273.6341   $273.63   $273.65   $273.60  
  Purchase #3 $49.91   10.317%   $55.0592   $55.06   $55.05   $55.10  
  Purchase #4 $210.94   12.608%   $237.5353   $237.54   $237.55   $237.50  
  Purchase #5 $234.76   11.709%   $262.248   $262.25   $262.25   $262.20  
  Purchase #6 $109.72   11.656%   $122.509   $122.51   $122.50   $122.50  
  Purchase #7 $191.66   13.358%   $217.2619   $217.26   $217.25   $217.30  
  7 purchase totals = $1,160.90       $1,287.9196   $1,287.92   $1,287.90   $1,287.90