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 $106.71   7.202%   $114.3953   $114.40   $114.40   $114.40  
  Purchase #2 $71.32   7.743%   $76.8423   $76.84   $76.85   $76.80  
  Purchase #3 $248.95   6.451%   $265.0098   $265.01   $265.00   $265.00  
  Purchase #4 $212.34   5.756%   $224.5623   $224.56   $224.55   $224.60  
  Purchase #5 $123.70   9.628%   $135.6098   $135.61   $135.60   $135.60  
  Purchase #6 $118.58   5.149%   $124.6857   $124.69   $124.70   $124.70  
  Purchase #7 $98.34   3.761%   $102.0386   $102.04   $102.05   $102.00  
  7 purchase totals = $979.94       $1,043.1438   $1,043.15   $1,043.15   $1,043.10