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 $241.97   7.159%   $259.2926   $259.29   $259.30   $259.30  
  Purchase #2 $117.61   3.871%   $122.1627   $122.16   $122.15   $122.20  
  Purchase #3 $192.36   13.208%   $217.7669   $217.77   $217.75   $217.80  
  Purchase #4 $114.49   7.327%   $122.8787   $122.88   $122.90   $122.90  
  Purchase #5 $234.79   12.261%   $263.5776   $263.58   $263.60   $263.60  
  Purchase #6 $119.72   11.329%   $133.2831   $133.28   $133.30   $133.30  
  Purchase #7 $194.80   12.105%   $218.3805   $218.38   $218.40   $218.40  
  7 purchase totals = $1,215.74       $1,337.3421   $1,337.34   $1,337.40   $1,337.50