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 $84.73   13.457%   $96.1321   $96.13   $96.15   $96.10  
  Purchase #2 $56.40   8.622%   $61.2628   $61.26   $61.25   $61.30  
  Purchase #3 $236.95   4.849%   $248.4397   $248.44   $248.45   $248.40  
  Purchase #4 $112.91   6.271%   $119.9906   $119.99   $120.00   $120.00  
  Purchase #5 $185.38   9.525%   $203.0374   $203.04   $203.05   $203.00  
  Purchase #6 $32.92   11.146%   $36.5893   $36.59   $36.60   $36.60  
  Purchase #7 $248.28   10.576%   $274.5381   $274.54   $274.55   $274.50  
  7 purchase totals = $957.57       $1,039.9900   $1,039.99   $1,040.05   $1,039.90