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 $76.25   11.772%   $85.2262   $85.23   $85.25   $85.20  
  Purchase #2 $156.41   13.586%   $177.6599   $177.66   $177.65   $177.70  
  Purchase #3 $192.53   11.515%   $214.6998   $214.70   $214.70   $214.70  
  Purchase #4 $151.34   13.440%   $171.6801   $171.68   $171.70   $171.70  
  Purchase #5 $37.29   8.858%   $40.5931   $40.59   $40.60   $40.60  
  Purchase #6 $171.85   9.573%   $188.3012   $188.30   $188.30   $188.30  
  Purchase #7 $107.60   6.225%   $114.2981   $114.30   $114.30   $114.30  
  7 purchase totals = $893.27       $992.4584   $992.46   $992.50   $992.50