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 $49.81   8.787%   $54.1868   $54.19   $54.20   $54.20  
  Purchase #2 $127.67   9.769%   $140.1421   $140.14   $140.15   $140.10  
  Purchase #3 $184.85   4.636%   $193.4196   $193.42   $193.40   $193.40  
  Purchase #4 $243.61   12.309%   $273.596   $273.60   $273.60   $273.60  
  Purchase #5 $241.69   5.798%   $255.7032   $255.70   $255.70   $255.70  
  Purchase #6 $182.32   4.543%   $190.6028   $190.60   $190.60   $190.60  
  Purchase #7 $250.74   3.791%   $260.2456   $260.25   $260.25   $260.20  
  7 purchase totals = $1,280.69       $1,367.8961   $1,367.90   $1,367.90   $1,367.80