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 $207.94   13.821%   $236.6794   $236.68   $236.70   $236.70  
  Purchase #2 $67.97   7.144%   $72.8258   $72.83   $72.85   $72.80  
  Purchase #3 $30.92   11.303%   $34.4149   $34.41   $34.40   $34.40  
  Purchase #4 $65.46   4.606%   $68.4751   $68.48   $68.50   $68.50  
  Purchase #5 $200.58   8.222%   $217.0717   $217.07   $217.05   $217.10  
  Purchase #6 $26.96   12.291%   $30.2737   $30.27   $30.25   $30.30  
  Purchase #7 $101.86   3.325%   $105.2468   $105.25   $105.25   $105.20  
  7 purchase totals = $701.69       $764.9874   $764.99   $765.00   $765.00