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 $49.75   13.619%   $56.5255   $56.53   $56.55   $56.50  
  Purchase #2 $124.32   4.238%   $129.5887   $129.59   $129.60   $129.60  
  Purchase #3 $113.63   7.597%   $122.2625   $122.26   $122.25   $122.30  
  Purchase #4 $69.72   8.290%   $75.4998   $75.50   $75.50   $75.50  
  Purchase #5 $157.86   10.866%   $175.0131   $175.01   $175.00   $175.00  
  Purchase #6 $158.93   6.149%   $168.7026   $168.70   $168.70   $168.70  
  Purchase #7 $27.25   5.587%   $28.7725   $28.77   $28.75   $28.80  
  7 purchase totals = $701.46       $756.3647   $756.36   $756.35   $756.40