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 $44.44   10.349%   $49.0391   $49.04   $49.05   $49.00  
  Purchase #2 $34.26   3.766%   $35.5502   $35.55   $35.55   $35.60  
  Purchase #3 $127.68   10.188%   $140.688   $140.69   $140.70   $140.70  
  Purchase #4 $230.97   10.405%   $255.0024   $255.00   $255.00   $255.00  
  Purchase #5 $97.72   11.777%   $109.2285   $109.23   $109.25   $109.20  
  Purchase #6 $205.50   8.394%   $222.7497   $222.75   $222.75   $222.70  
  Purchase #7 $105.73   8.547%   $114.7667   $114.77   $114.75   $114.80  
  7 purchase totals = $846.30       $927.0246   $927.03   $927.05   $927.00