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 $216.75   10.480%   $239.4654   $239.47   $239.45   $239.50  
  Purchase #2 $221.38   11.119%   $245.9952   $246.00   $246.00   $246.00  
  Purchase #3 $33.54   9.298%   $36.6585   $36.66   $36.65   $36.70  
  Purchase #4 $36.91   11.764%   $41.2521   $41.25   $41.25   $41.30  
  Purchase #5 $161.96   7.168%   $173.5693   $173.57   $173.55   $173.60  
  Purchase #6 $46.76   9.639%   $51.2672   $51.27   $51.25   $51.30  
  Purchase #7 $190.40   4.356%   $198.6938   $198.69   $198.70   $198.70  
  7 purchase totals = $907.70       $986.9015   $986.91   $986.85   $987.10