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 $239.81   12.267%   $269.2275   $269.23   $269.25   $269.20  
  Purchase #2 $194.52   3.103%   $200.556   $200.56   $200.55   $200.60  
  Purchase #3 $89.39   7.120%   $95.7546   $95.75   $95.75   $95.80  
  Purchase #4 $216.60   12.202%   $243.0295   $243.03   $243.05   $243.00  
  Purchase #5 $50.82   4.495%   $53.1044   $53.10   $53.10   $53.10  
  Purchase #6 $114.70   8.565%   $124.5241   $124.52   $124.50   $124.50  
  Purchase #7 $136.29   3.405%   $140.9307   $140.93   $140.95   $140.90  
  7 purchase totals = $1,042.13       $1,127.1268   $1,127.12   $1,127.15   $1,127.10