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 $239.67   7.462%   $257.5542   $257.55   $257.55   $257.60  
  Purchase #2 $63.37   9.108%   $69.1417   $69.14   $69.15   $69.10  
  Purchase #3 $169.86   13.167%   $192.2255   $192.23   $192.25   $192.20  
  Purchase #4 $109.70   5.405%   $115.6293   $115.63   $115.65   $115.60  
  Purchase #5 $226.61   10.758%   $250.9887   $250.99   $251.00   $251.00  
  Purchase #6 $57.96   9.507%   $63.4703   $63.47   $63.45   $63.50  
  Purchase #7 $62.79   11.373%   $69.9311   $69.93   $69.95   $69.90  
  7 purchase totals = $929.96       $1,018.9408   $1,018.94   $1,019.00   $1,018.90