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 $104.67   6.429%   $111.3992   $111.40   $111.40   $111.40  
  Purchase #2 $162.56   8.607%   $176.5515   $176.55   $176.55   $176.60  
  Purchase #3 $11.33   10.190%   $12.4845   $12.48   $12.50   $12.50  
  Purchase #4 $183.99   12.274%   $206.5729   $206.57   $206.55   $206.60  
  Purchase #5 $53.87   7.239%   $57.7696   $57.77   $57.75   $57.80  
  Purchase #6 $114.27   6.850%   $122.0975   $122.10   $122.10   $122.10  
  Purchase #7 $81.89   5.622%   $86.4939   $86.49   $86.50   $86.50  
  7 purchase totals = $712.58       $773.3691   $773.36   $773.35   $773.50