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 $203.41   6.791%   $217.2236   $217.22   $217.20   $217.20  
  Purchase #2 $240.66   9.423%   $263.3374   $263.34   $263.35   $263.30  
  Purchase #3 $8.25   4.139%   $8.5915   $8.59   $8.60   $8.60  
  Purchase #4 $217.43   12.659%   $244.9545   $244.95   $244.95   $245.00  
  Purchase #5 $52.38   3.579%   $54.2547   $54.25   $54.25   $54.30  
  Purchase #6 $43.44   10.225%   $47.8817   $47.88   $47.90   $47.90  
  Purchase #7 $224.91   11.449%   $250.6599   $250.66   $250.65   $250.70  
  7 purchase totals = $990.48       $1,086.9033   $1,086.89   $1,086.90   $1,087.00