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 $196.87   5.116%   $206.9419   $206.94   $206.95   $206.90  
  Purchase #2 $103.93   10.331%   $114.667   $114.67   $114.65   $114.70  
  Purchase #3 $241.59   9.452%   $264.4251   $264.43   $264.45   $264.40  
  Purchase #4 $208.74   9.349%   $228.2551   $228.26   $228.25   $228.30  
  Purchase #5 $237.69   7.298%   $255.0366   $255.04   $255.05   $255.00  
  Purchase #6 $164.65   11.664%   $183.8548   $183.85   $183.85   $183.90  
  Purchase #7 $83.60   13.256%   $94.682   $94.68   $94.70   $94.70  
  7 purchase totals = $1,237.07       $1,347.8625   $1,347.87   $1,347.90   $1,347.90