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 $238.99   12.812%   $269.6094   $269.61   $269.60   $269.60  
  Purchase #2 $88.97   7.455%   $95.6027   $95.60   $95.60   $95.60  
  Purchase #3 $14.44   6.320%   $15.3526   $15.35   $15.35   $15.40  
  Purchase #4 $173.57   9.721%   $190.4427   $190.44   $190.45   $190.40  
  Purchase #5 $89.41   8.770%   $97.2513   $97.25   $97.25   $97.30  
  Purchase #6 $176.99   3.568%   $183.305   $183.31   $183.30   $183.30  
  Purchase #7 $247.67   6.674%   $264.1995   $264.20   $264.20   $264.20  
  7 purchase totals = $1,030.04       $1,115.7632   $1,115.76   $1,115.75   $1,115.80