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 $200.41   11.193%   $222.8419   $222.84   $222.85   $222.80  
  Purchase #2 $144.58   12.161%   $162.1624   $162.16   $162.15   $162.20  
  Purchase #3 $23.64   11.464%   $26.3501   $26.35   $26.35   $26.40  
  Purchase #4 $124.32   7.294%   $133.3879   $133.39   $133.40   $133.40  
  Purchase #5 $77.89   5.662%   $82.3001   $82.30   $82.30   $82.30  
  Purchase #6 $190.42   3.759%   $197.5779   $197.58   $197.60   $197.60  
  Purchase #7 $166.77   3.361%   $172.3751   $172.38   $172.40   $172.40  
  7 purchase totals = $928.03       $996.9954   $997.00   $997.05   $997.10