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 $210.41   13.847%   $239.5455   $239.55   $239.55   $239.50  
  Purchase #2 $142.40   8.451%   $154.4342   $154.43   $154.45   $154.40  
  Purchase #3 $132.25   9.284%   $144.5281   $144.53   $144.55   $144.50  
  Purchase #4 $134.37   11.253%   $149.4907   $149.49   $149.50   $149.50  
  Purchase #5 $217.62   4.641%   $227.7197   $227.72   $227.70   $227.70  
  Purchase #6 $68.83   10.809%   $76.2698   $76.27   $76.25   $76.30  
  Purchase #7 $40.31   7.737%   $43.4288   $43.43   $43.45   $43.40  
  7 purchase totals = $946.19       $1,035.4168   $1,035.42   $1,035.45   $1,035.30