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 $213.73   9.292%   $233.5898   $233.59   $233.60   $233.60  
  Purchase #2 $184.55   12.528%   $207.6704   $207.67   $207.65   $207.70  
  Purchase #3 $85.26   6.455%   $90.7635   $90.76   $90.75   $90.80  
  Purchase #4 $173.85   5.598%   $183.5821   $183.58   $183.60   $183.60  
  Purchase #5 $178.81   6.401%   $190.2556   $190.26   $190.25   $190.30  
  Purchase #6 $175.33   13.738%   $199.4168   $199.42   $199.40   $199.40  
  Purchase #7 $233.61   6.749%   $249.3763   $249.38   $249.40   $249.40  
  7 purchase totals = $1,245.14       $1,354.6545   $1,354.66   $1,354.65   $1,354.80