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 $214.62   3.643%   $222.4386   $222.44   $222.45   $222.40  
  Purchase #2 $34.87   5.871%   $36.9172   $36.92   $36.90   $36.90  
  Purchase #3 $164.76   5.811%   $174.3342   $174.33   $174.35   $174.30  
  Purchase #4 $56.58   11.115%   $62.8689   $62.87   $62.85   $62.90  
  Purchase #5 $203.87   8.195%   $220.5771   $220.58   $220.60   $220.60  
  Purchase #6 $157.46   4.406%   $164.3977   $164.40   $164.40   $164.40  
  Purchase #7 $23.87   3.526%   $24.7117   $24.71   $24.70   $24.70  
  7 purchase totals = $856.03       $906.2454   $906.25   $906.25   $906.20