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 $24.71   3.365%   $25.5415   $25.54   $25.55   $25.50  
  Purchase #2 $208.36   13.823%   $237.1616   $237.16   $237.15   $237.20  
  Purchase #3 $104.85   9.216%   $114.513   $114.51   $114.50   $114.50  
  Purchase #4 $205.48   6.420%   $218.6718   $218.67   $218.65   $218.70  
  Purchase #5 $208.49   8.280%   $225.753   $225.75   $225.75   $225.80  
  Purchase #6 $60.51   3.160%   $62.4221   $62.42   $62.40   $62.40  
  Purchase #7 $143.81   9.572%   $157.5755   $157.58   $157.60   $157.60  
  7 purchase totals = $956.21       $1,041.6385   $1,041.63   $1,041.60   $1,041.70