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 $207.60   6.838%   $221.7957   $221.80   $221.80   $221.80  
  Purchase #2 $47.38   12.334%   $53.2238   $53.22   $53.20   $53.20  
  Purchase #3 $140.63   12.106%   $157.6547   $157.65   $157.65   $157.70  
  Purchase #4 $221.61   9.466%   $242.5876   $242.59   $242.60   $242.60  
  Purchase #5 $60.91   5.118%   $64.0274   $64.03   $64.05   $64.00  
  Purchase #6 $249.78   11.460%   $278.4048   $278.40   $278.40   $278.40  
  Purchase #7 $54.26   4.600%   $56.756   $56.76   $56.75   $56.80  
  7 purchase totals = $982.17       $1,074.4500   $1,074.45   $1,074.45   $1,074.50