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 $114.97   7.637%   $123.7503   $123.75   $123.75   $123.80  
  Purchase #2 $13.34   7.132%   $14.2914   $14.29   $14.30   $14.30  
  Purchase #3 $94.90   6.453%   $101.0239   $101.02   $101.00   $101.00  
  Purchase #4 $248.25   10.488%   $274.2865   $274.29   $274.30   $274.30  
  Purchase #5 $174.29   6.280%   $185.2354   $185.24   $185.25   $185.20  
  Purchase #6 $187.81   13.202%   $212.6047   $212.60   $212.60   $212.60  
  Purchase #7 $148.69   10.382%   $164.127   $164.13   $164.15   $164.10  
  7 purchase totals = $982.25       $1,075.3192   $1,075.32   $1,075.35   $1,075.30