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 $229.97   8.116%   $248.6344   $248.63   $248.65   $248.60  
  Purchase #2 $146.63   5.244%   $154.3193   $154.32   $154.30   $154.30  
  Purchase #3 $227.70   8.272%   $246.5353   $246.54   $246.55   $246.50  
  Purchase #4 $58.40   5.873%   $61.8298   $61.83   $61.85   $61.80  
  Purchase #5 $147.95   8.858%   $161.0554   $161.06   $161.05   $161.10  
  Purchase #6 $164.65   12.688%   $185.5408   $185.54   $185.55   $185.50  
  Purchase #7 $244.59   10.703%   $270.7685   $270.77   $270.75   $270.80  
  7 purchase totals = $1,219.89       $1,328.6835   $1,328.69   $1,328.70   $1,328.60