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 $92.37   9.545%   $101.1867   $101.19   $101.20   $101.20  
  Purchase #2 $241.45   4.744%   $252.9044   $252.90   $252.90   $252.90  
  Purchase #3 $140.55   12.349%   $157.9065   $157.91   $157.90   $157.90  
  Purchase #4 $173.72   6.755%   $185.4548   $185.45   $185.45   $185.50  
  Purchase #5 $75.34   7.844%   $81.2497   $81.25   $81.25   $81.20  
  Purchase #6 $244.27   12.545%   $274.9137   $274.91   $274.90   $274.90  
  Purchase #7 $29.75   12.243%   $33.3923   $33.39   $33.40   $33.40  
  7 purchase totals = $997.45       $1,087.0081   $1,087.00   $1,087.00   $1,087.00