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 $120.95   4.396%   $126.267   $126.27   $126.25   $126.30  
  Purchase #2 $70.40   8.713%   $76.534   $76.53   $76.55   $76.50  
  Purchase #3 $81.81   13.613%   $92.9468   $92.95   $92.95   $92.90  
  Purchase #4 $122.76   11.634%   $137.0419   $137.04   $137.05   $137.00  
  Purchase #5 $181.69   10.132%   $200.0988   $200.10   $200.10   $200.10  
  Purchase #6 $237.36   13.782%   $270.073   $270.07   $270.05   $270.10  
  Purchase #7 $151.31   7.602%   $162.8126   $162.81   $162.80   $162.80  
  7 purchase totals = $966.28       $1,065.7741   $1,065.77   $1,065.75   $1,065.70