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 $44.74   5.667%   $47.2754   $47.28   $47.30   $47.30  
  Purchase #2 $217.85   9.785%   $239.1666   $239.17   $239.15   $239.20  
  Purchase #3 $60.55   6.392%   $64.4204   $64.42   $64.40   $64.40  
  Purchase #4 $231.55   8.235%   $250.6181   $250.62   $250.60   $250.60  
  Purchase #5 $113.70   7.535%   $122.2673   $122.27   $122.25   $122.30  
  Purchase #6 $190.81   5.181%   $200.6959   $200.70   $200.70   $200.70  
  Purchase #7 $31.34   11.319%   $34.8874   $34.89   $34.90   $34.90  
  7 purchase totals = $890.54       $959.3311   $959.35   $959.30   $959.40