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 $242.79   4.302%   $253.2348   $253.23   $253.25   $253.20  
  Purchase #2 $174.43   6.799%   $186.2895   $186.29   $186.30   $186.30  
  Purchase #3 $62.41   3.186%   $64.3984   $64.40   $64.40   $64.40  
  Purchase #4 $77.99   6.770%   $83.2699   $83.27   $83.25   $83.30  
  Purchase #5 $95.32   13.190%   $107.8927   $107.89   $107.90   $107.90  
  Purchase #6 $109.72   4.126%   $114.247   $114.25   $114.25   $114.20  
  Purchase #7 $119.99   6.716%   $128.0485   $128.05   $128.05   $128.00  
  7 purchase totals = $882.65       $937.3808   $937.38   $937.40   $937.30