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 $207.29   8.612%   $225.1418   $225.14   $225.15   $225.10  
  Purchase #2 $67.66   5.320%   $71.2595   $71.26   $71.25   $71.30  
  Purchase #3 $101.28   13.281%   $114.731   $114.73   $114.75   $114.70  
  Purchase #4 $240.83   5.493%   $254.0588   $254.06   $254.05   $254.10  
  Purchase #5 $153.40   10.180%   $169.0161   $169.02   $169.00   $169.00  
  Purchase #6 $41.59   13.362%   $47.1473   $47.15   $47.15   $47.10  
  Purchase #7 $133.58   5.853%   $141.3984   $141.40   $141.40   $141.40  
  7 purchase totals = $945.63       $1,022.7529   $1,022.76   $1,022.75   $1,022.70