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 $225.72   6.779%   $241.0216   $241.02   $241.00   $241.00  
  Purchase #2 $98.87   5.535%   $104.3425   $104.34   $104.35   $104.30  
  Purchase #3 $41.70   12.482%   $46.905   $46.91   $46.90   $46.90  
  Purchase #4 $198.88   3.700%   $206.2386   $206.24   $206.25   $206.20  
  Purchase #5 $168.63   10.509%   $186.3513   $186.35   $186.35   $186.40  
  Purchase #6 $237.76   5.318%   $250.4041   $250.40   $250.40   $250.40  
  Purchase #7 $57.47   11.749%   $64.2222   $64.22   $64.20   $64.20  
  7 purchase totals = $1,029.03       $1,099.4853   $1,099.48   $1,099.45   $1,099.40