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 $244.27   8.493%   $265.0159   $265.02   $265.00   $265.00  
  Purchase #2 $55.62   3.327%   $57.4705   $57.47   $57.45   $57.50  
  Purchase #3 $192.88   5.189%   $202.8885   $202.89   $202.90   $202.90  
  Purchase #4 $11.55   7.646%   $12.4331   $12.43   $12.45   $12.40  
  Purchase #5 $83.63   12.842%   $94.3698   $94.37   $94.35   $94.40  
  Purchase #6 $94.38   3.652%   $97.8268   $97.83   $97.85   $97.80  
  Purchase #7 $211.49   4.691%   $221.411   $221.41   $221.40   $221.40  
  7 purchase totals = $893.82       $951.4156   $951.42   $951.40   $951.40