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 $242.88   10.538%   $268.4747   $268.47   $268.45   $268.50  
  Purchase #2 $220.72   13.593%   $250.7225   $250.72   $250.70   $250.70  
  Purchase #3 $91.32   13.834%   $103.9532   $103.95   $103.95   $104.00  
  Purchase #4 $174.99   12.600%   $197.0387   $197.04   $197.05   $197.00  
  Purchase #5 $59.77   5.630%   $63.1351   $63.14   $63.15   $63.10  
  Purchase #6 $139.98   9.379%   $153.1087   $153.11   $153.10   $153.10  
  Purchase #7 $16.66   3.672%   $17.2718   $17.27   $17.25   $17.30  
  7 purchase totals = $946.32       $1,053.7047   $1,053.70   $1,053.65   $1,053.70