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 $208.31   4.176%   $217.009   $217.01   $217.00   $217.00  
  Purchase #2 $44.71   6.602%   $47.6618   $47.66   $47.65   $47.70  
  Purchase #3 $173.68   11.702%   $194.004   $194.00   $194.00   $194.00  
  Purchase #4 $216.49   4.683%   $226.6282   $226.63   $226.65   $226.60  
  Purchase #5 $250.72   3.378%   $259.1893   $259.19   $259.20   $259.20  
  Purchase #6 $15.27   8.732%   $16.6034   $16.60   $16.60   $16.60  
  Purchase #7 $24.62   6.138%   $26.1312   $26.13   $26.15   $26.10  
  7 purchase totals = $933.80       $987.2269   $987.22   $987.25   $987.20