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 $228.56   3.151%   $235.7619   $235.76   $235.75   $235.80  
  Purchase #2 $37.74   10.376%   $41.6559   $41.66   $41.65   $41.70  
  Purchase #3 $107.34   6.668%   $114.4974   $114.50   $114.50   $114.50  
  Purchase #4 $118.27   10.267%   $130.4128   $130.41   $130.40   $130.40  
  Purchase #5 $202.83   13.568%   $230.35   $230.35   $230.35   $230.40  
  Purchase #6 $248.68   5.527%   $262.4245   $262.42   $262.40   $262.40  
  Purchase #7 $24.33   3.571%   $25.1988   $25.20   $25.20   $25.20  
  7 purchase totals = $967.75       $1,040.3013   $1,040.30   $1,040.25   $1,040.40