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 $23.47   11.849%   $26.251   $26.25   $26.25   $26.30  
  Purchase #2 $109.77   13.339%   $124.4122   $124.41   $124.40   $124.40  
  Purchase #3 $5.44   6.346%   $5.7852   $5.79   $5.80   $5.80  
  Purchase #4 $214.83   12.723%   $242.1628   $242.16   $242.15   $242.20  
  Purchase #5 $50.76   12.125%   $56.9147   $56.91   $56.90   $56.90  
  Purchase #6 $240.67   11.174%   $267.5625   $267.56   $267.55   $267.60  
  Purchase #7 $47.84   5.242%   $50.3478   $50.35   $50.35   $50.30  
  7 purchase totals = $692.78       $773.4362   $773.43   $773.40   $773.50