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 $76.33   10.847%   $84.6095   $84.61   $84.60   $84.60  
  Purchase #2 $113.32   8.704%   $123.1834   $123.18   $123.20   $123.20  
  Purchase #3 $43.70   5.711%   $46.1957   $46.20   $46.20   $46.20  
  Purchase #4 $10.92   10.575%   $12.0748   $12.07   $12.05   $12.10  
  Purchase #5 $231.93   4.319%   $241.9471   $241.95   $241.95   $241.90  
  Purchase #6 $196.67   9.131%   $214.6279   $214.63   $214.65   $214.60  
  Purchase #7 $49.58   4.338%   $51.7308   $51.73   $51.75   $51.70  
  7 purchase totals = $722.45       $774.3692   $774.37   $774.40   $774.30