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 $202.44   3.102%   $208.7197   $208.72   $208.70   $208.70  
  Purchase #2 $41.71   6.186%   $44.2902   $44.29   $44.30   $44.30  
  Purchase #3 $126.85   5.572%   $133.9181   $133.92   $133.90   $133.90  
  Purchase #4 $157.89   3.555%   $163.503   $163.50   $163.50   $163.50  
  Purchase #5 $239.38   13.431%   $271.5311   $271.53   $271.55   $271.50  
  Purchase #6 $134.46   4.604%   $140.6505   $140.65   $140.65   $140.70  
  Purchase #7 $85.98   8.529%   $93.3132   $93.31   $93.30   $93.30  
  7 purchase totals = $988.71       $1,055.9258   $1,055.92   $1,055.90   $1,055.90