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 $59.97   4.866%   $62.8881   $62.89   $62.90   $62.90  
  Purchase #2 $22.50   13.589%   $25.5575   $25.56   $25.55   $25.60  
  Purchase #3 $68.27   13.809%   $77.6974   $77.70   $77.70   $77.70  
  Purchase #4 $38.74   6.537%   $41.2724   $41.27   $41.25   $41.30  
  Purchase #5 $92.87   13.464%   $105.374   $105.37   $105.35   $105.40  
  Purchase #6 $202.48   5.533%   $213.6832   $213.68   $213.70   $213.70  
  Purchase #7 $53.81   7.239%   $57.7053   $57.71   $57.70   $57.70  
  7 purchase totals = $538.64       $584.1779   $584.18   $584.15   $584.30