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 $201.27   11.308%   $224.0296   $224.03   $224.05   $224.00  
  Purchase #2 $249.28   4.287%   $259.9666   $259.97   $259.95   $260.00  
  Purchase #3 $104.89   3.579%   $108.644   $108.64   $108.65   $108.60  
  Purchase #4 $171.51   8.196%   $185.567   $185.57   $185.55   $185.60  
  Purchase #5 $173.62   13.801%   $197.5813   $197.58   $197.60   $197.60  
  Purchase #6 $192.65   11.223%   $214.2711   $214.27   $214.25   $214.30  
  Purchase #7 $119.37   10.333%   $131.7045   $131.70   $131.70   $131.70  
  7 purchase totals = $1,212.59       $1,321.7641   $1,321.76   $1,321.75   $1,321.80