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 $36.69   6.152%   $38.9472   $38.95   $38.95   $38.90  
  Purchase #2 $228.39   8.723%   $248.3125   $248.31   $248.30   $248.30  
  Purchase #3 $109.43   6.509%   $116.5528   $116.55   $116.55   $116.60  
  Purchase #4 $155.55   13.329%   $176.2833   $176.28   $176.30   $176.30  
  Purchase #5 $85.96   6.270%   $91.3497   $91.35   $91.35   $91.30  
  Purchase #6 $142.25   8.830%   $154.8107   $154.81   $154.80   $154.80  
  Purchase #7 $206.97   7.358%   $222.1989   $222.20   $222.20   $222.20  
  7 purchase totals = $965.24       $1,048.4551   $1,048.45   $1,048.45   $1,048.40