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 $237.42   10.450%   $262.2304   $262.23   $262.25   $262.20  
  Purchase #2 $177.26   5.752%   $187.456   $187.46   $187.45   $187.50  
  Purchase #3 $95.53   12.739%   $107.6996   $107.70   $107.70   $107.70  
  Purchase #4 $226.59   11.834%   $253.4047   $253.40   $253.40   $253.40  
  Purchase #5 $44.61   6.586%   $47.548   $47.55   $47.55   $47.50  
  Purchase #6 $246.61   12.207%   $276.7137   $276.71   $276.70   $276.70  
  Purchase #7 $233.79   9.608%   $256.2525   $256.25   $256.25   $256.30  
  7 purchase totals = $1,261.81       $1,391.3049   $1,391.30   $1,391.30   $1,391.30