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 $231.30   11.862%   $258.7368   $258.74   $258.75   $258.70  
  Purchase #2 $169.27   9.571%   $185.4708   $185.47   $185.45   $185.50  
  Purchase #3 $62.87   6.194%   $66.7642   $66.76   $66.75   $66.80  
  Purchase #4 $95.49   7.540%   $102.6899   $102.69   $102.70   $102.70  
  Purchase #5 $29.68   13.491%   $33.6841   $33.68   $33.70   $33.70  
  Purchase #6 $164.97   4.613%   $172.5801   $172.58   $172.60   $172.60  
  Purchase #7 $236.40   4.527%   $247.1018   $247.10   $247.10   $247.10  
  7 purchase totals = $989.98       $1,067.0277   $1,067.02   $1,067.05   $1,067.10