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 $24.37   4.373%   $25.4357   $25.44   $25.45   $25.40  
  Purchase #2 $249.26   5.346%   $262.5854   $262.59   $262.60   $262.60  
  Purchase #3 $60.64   7.274%   $65.051   $65.05   $65.05   $65.10  
  Purchase #4 $135.53   9.437%   $148.32   $148.32   $148.30   $148.30  
  Purchase #5 $39.87   9.581%   $43.6899   $43.69   $43.70   $43.70  
  Purchase #6 $18.80   13.215%   $21.2844   $21.28   $21.30   $21.30  
  Purchase #7 $224.61   5.790%   $237.6149   $237.61   $237.60   $237.60  
  7 purchase totals = $753.08       $803.9813   $803.98   $804.00   $804.00