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 $185.25   11.387%   $206.3444   $206.34   $206.35   $206.30  
  Purchase #2 $104.68   7.684%   $112.7236   $112.72   $112.70   $112.70  
  Purchase #3 $200.55   9.576%   $219.7547   $219.75   $219.75   $219.80  
  Purchase #4 $226.57   9.758%   $248.6787   $248.68   $248.70   $248.70  
  Purchase #5 $22.35   10.468%   $24.6896   $24.69   $24.70   $24.70  
  Purchase #6 $10.93   8.670%   $11.8776   $11.88   $11.90   $11.90  
  Purchase #7 $168.68   11.274%   $187.697   $187.70   $187.70   $187.70  
  7 purchase totals = $919.01       $1,011.7656   $1,011.76   $1,011.80   $1,011.80