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 $248.51   5.263%   $261.5891   $261.59   $261.60   $261.60  
  Purchase #2 $233.27   12.504%   $262.4381   $262.44   $262.45   $262.40  
  Purchase #3 $144.71   4.486%   $151.2017   $151.20   $151.20   $151.20  
  Purchase #4 $157.37   7.378%   $168.9808   $168.98   $169.00   $169.00  
  Purchase #5 $156.93   4.669%   $164.2571   $164.26   $164.25   $164.30  
  Purchase #6 $46.61   6.503%   $49.641   $49.64   $49.65   $49.60  
  Purchase #7 $170.86   10.849%   $189.3966   $189.40   $189.40   $189.40  
  7 purchase totals = $1,158.26       $1,247.5044   $1,247.51   $1,247.55   $1,247.50