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 $45.68   6.161%   $48.4943   $48.49   $48.50   $48.50  
  Purchase #2 $153.27   7.160%   $164.2441   $164.24   $164.25   $164.20  
  Purchase #3 $56.55   10.716%   $62.6099   $62.61   $62.60   $62.60  
  Purchase #4 $126.36   8.863%   $137.5593   $137.56   $137.55   $137.60  
  Purchase #5 $167.75   10.460%   $185.2967   $185.30   $185.30   $185.30  
  Purchase #6 $220.87   8.328%   $239.2641   $239.26   $239.25   $239.30  
  Purchase #7 $56.68   6.628%   $60.4368   $60.44   $60.45   $60.40  
  7 purchase totals = $827.16       $897.9052   $897.90   $897.90   $897.90