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 $38.59   12.724%   $43.5002   $43.50   $43.50   $43.50  
  Purchase #2 $63.31   6.311%   $67.3055   $67.31   $67.30   $67.30  
  Purchase #3 $126.81   5.548%   $133.8454   $133.85   $133.85   $133.80  
  Purchase #4 $86.31   9.694%   $94.6769   $94.68   $94.70   $94.70  
  Purchase #5 $87.49   12.258%   $98.2145   $98.21   $98.20   $98.20  
  Purchase #6 $206.88   6.703%   $220.7472   $220.75   $220.75   $220.70  
  Purchase #7 $64.61   7.179%   $69.2484   $69.25   $69.25   $69.20  
  7 purchase totals = $674.00       $727.5381   $727.55   $727.55   $727.40