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 $119.41   5.669%   $126.1794   $126.18   $126.20   $126.20  
  Purchase #2 $158.43   8.257%   $171.5116   $171.51   $171.50   $171.50  
  Purchase #3 $50.49   11.864%   $56.4801   $56.48   $56.50   $56.50  
  Purchase #4 $173.90   13.358%   $197.1296   $197.13   $197.15   $197.10  
  Purchase #5 $221.43   13.225%   $250.7141   $250.71   $250.70   $250.70  
  Purchase #6 $57.28   4.820%   $60.0409   $60.04   $60.05   $60.00  
  Purchase #7 $179.87   13.381%   $203.9384   $203.94   $203.95   $203.90  
  7 purchase totals = $960.81       $1,065.9941   $1,065.99   $1,066.05   $1,065.90