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 $248.43   11.193%   $276.2368   $276.24   $276.25   $276.20  
  Purchase #2 $103.34   11.135%   $114.8469   $114.85   $114.85   $114.80  
  Purchase #3 $62.42   4.197%   $65.0398   $65.04   $65.05   $65.00  
  Purchase #4 $233.93   10.246%   $257.8985   $257.90   $257.90   $257.90  
  Purchase #5 $177.92   9.798%   $195.3526   $195.35   $195.35   $195.40  
  Purchase #6 $120.61   9.797%   $132.4262   $132.43   $132.45   $132.40  
  Purchase #7 $204.25   11.325%   $227.3813   $227.38   $227.40   $227.40  
  7 purchase totals = $1,150.90       $1,269.1821   $1,269.19   $1,269.25   $1,269.10