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 $24.59   6.718%   $26.242   $26.24   $26.25   $26.20  
  Purchase #2 $58.64   4.342%   $61.1861   $61.19   $61.20   $61.20  
  Purchase #3 $114.74   10.543%   $126.837   $126.84   $126.85   $126.80  
  Purchase #4 $111.84   7.688%   $120.4383   $120.44   $120.45   $120.40  
  Purchase #5 $156.44   5.394%   $164.8784   $164.88   $164.90   $164.90  
  Purchase #6 $15.29   9.226%   $16.7007   $16.70   $16.70   $16.70  
  Purchase #7 $141.74   13.697%   $161.1541   $161.15   $161.15   $161.20  
  7 purchase totals = $623.28       $677.4366   $677.44   $677.50   $677.40