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 $221.51   10.571%   $244.9258   $244.93   $244.95   $244.90  
  Purchase #2 $53.34   10.292%   $58.8298   $58.83   $58.85   $58.80  
  Purchase #3 $156.36   9.526%   $171.2549   $171.25   $171.25   $171.30  
  Purchase #4 $248.57   5.832%   $263.0666   $263.07   $263.05   $263.10  
  Purchase #5 $175.69   11.661%   $196.1772   $196.18   $196.20   $196.20  
  Purchase #6 $64.54   10.263%   $71.1637   $71.16   $71.15   $71.20  
  Purchase #7 $197.49   8.612%   $214.4978   $214.50   $214.50   $214.50  
  7 purchase totals = $1,117.50       $1,219.9158   $1,219.92   $1,219.95   $1,220.00