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 $109.39   12.226%   $122.764   $122.76   $122.75   $122.80  
  Purchase #2 $64.98   12.732%   $73.2533   $73.25   $73.25   $73.30  
  Purchase #3 $71.90   8.665%   $78.1301   $78.13   $78.15   $78.10  
  Purchase #4 $157.63   7.811%   $169.9425   $169.94   $169.95   $169.90  
  Purchase #5 $168.66   5.433%   $177.8233   $177.82   $177.80   $177.80  
  Purchase #6 $135.99   4.729%   $142.421   $142.42   $142.40   $142.40  
  Purchase #7 $147.39   11.317%   $164.0701   $164.07   $164.05   $164.10  
  7 purchase totals = $855.94       $928.4043   $928.39   $928.35   $928.40