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 $85.38   12.786%   $96.2967   $96.30   $96.30   $96.30  
  Purchase #2 $230.60   10.503%   $254.8199   $254.82   $254.80   $254.80  
  Purchase #3 $65.26   11.227%   $72.5867   $72.59   $72.60   $72.60  
  Purchase #4 $233.31   12.546%   $262.5811   $262.58   $262.60   $262.60  
  Purchase #5 $17.41   4.863%   $18.2566   $18.26   $18.25   $18.30  
  Purchase #6 $203.58   8.440%   $220.7622   $220.76   $220.75   $220.80  
  Purchase #7 $34.44   12.335%   $38.6882   $38.69   $38.70   $38.70  
  7 purchase totals = $869.98       $963.9914   $964.00   $964.00   $964.10