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 $82.39   13.618%   $93.6099   $93.61   $93.60   $93.60  
  Purchase #2 $173.36   11.432%   $193.1785   $193.18   $193.20   $193.20  
  Purchase #3 $49.40   6.683%   $52.7014   $52.70   $52.70   $52.70  
  Purchase #4 $53.28   5.606%   $56.2669   $56.27   $56.25   $56.30  
  Purchase #5 $76.70   6.263%   $81.5037   $81.50   $81.50   $81.50  
  Purchase #6 $79.62   9.152%   $86.9068   $86.91   $86.90   $86.90  
  Purchase #7 $121.69   5.109%   $127.9071   $127.91   $127.90   $127.90  
  7 purchase totals = $636.44       $692.0743   $692.08   $692.05   $692.10