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 $241.85   8.168%   $261.6043   $261.60   $261.60   $261.60  
  Purchase #2 $63.93   8.642%   $69.4548   $69.45   $69.45   $69.50  
  Purchase #3 $214.36   4.528%   $224.0662   $224.07   $224.05   $224.10  
  Purchase #4 $164.90   12.355%   $185.2734   $185.27   $185.25   $185.30  
  Purchase #5 $164.90   11.819%   $184.3895   $184.39   $184.40   $184.40  
  Purchase #6 $149.47   13.871%   $170.203   $170.20   $170.20   $170.20  
  Purchase #7 $157.36   4.446%   $164.3562   $164.36   $164.35   $164.40  
  7 purchase totals = $1,156.77       $1,259.3474   $1,259.34   $1,259.30   $1,259.50