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 $39.59   12.222%   $44.4287   $44.43   $44.45   $44.40  
  Purchase #2 $167.78   4.796%   $175.8267   $175.83   $175.85   $175.80  
  Purchase #3 $208.91   7.475%   $224.526   $224.53   $224.55   $224.50  
  Purchase #4 $182.78   4.638%   $191.2573   $191.26   $191.25   $191.30  
  Purchase #5 $29.72   6.420%   $31.628   $31.63   $31.65   $31.60  
  Purchase #6 $65.47   3.536%   $67.785   $67.79   $67.80   $67.80  
  Purchase #7 $225.87   10.157%   $248.8116   $248.81   $248.80   $248.80  
  7 purchase totals = $920.12       $984.2633   $984.28   $984.35   $984.20