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 $47.84   7.730%   $51.538   $51.54   $51.55   $51.50  
  Purchase #2 $147.83   7.859%   $159.448   $159.45   $159.45   $159.40  
  Purchase #3 $57.55   12.209%   $64.5763   $64.58   $64.60   $64.60  
  Purchase #4 $168.74   9.792%   $185.263   $185.26   $185.25   $185.30  
  Purchase #5 $73.47   10.113%   $80.9   $80.90   $80.90   $80.90  
  Purchase #6 $154.93   8.714%   $168.4306   $168.43   $168.45   $168.40  
  Purchase #7 $6.68   5.260%   $7.0314   $7.03   $7.05   $7.00  
  7 purchase totals = $657.04       $717.1873   $717.19   $717.25   $717.10