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 $14.63   13.313%   $16.5777   $16.58   $16.60   $16.60  
  Purchase #2 $153.58   12.811%   $173.2551   $173.26   $173.25   $173.30  
  Purchase #3 $177.90   8.115%   $192.3366   $192.34   $192.35   $192.30  
  Purchase #4 $213.62   5.678%   $225.7493   $225.75   $225.75   $225.70  
  Purchase #5 $59.27   7.309%   $63.602   $63.60   $63.60   $63.60  
  Purchase #6 $166.82   9.783%   $183.14   $183.14   $183.15   $183.10  
  Purchase #7 $105.44   10.872%   $116.9034   $116.90   $116.90   $116.90  
  7 purchase totals = $891.26       $971.5641   $971.57   $971.60   $971.50