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 $104.65   12.793%   $118.0379   $118.04   $118.05   $118.00  
  Purchase #2 $13.47   8.420%   $14.6042   $14.60   $14.60   $14.60  
  Purchase #3 $197.99   4.759%   $207.4123   $207.41   $207.40   $207.40  
  Purchase #4 $24.51   6.579%   $26.1225   $26.12   $26.10   $26.10  
  Purchase #5 $200.64   13.406%   $227.5378   $227.54   $227.55   $227.50  
  Purchase #6 $148.81   6.679%   $158.749   $158.75   $158.75   $158.70  
  Purchase #7 $214.91   5.299%   $226.2981   $226.30   $226.30   $226.30  
  7 purchase totals = $904.98       $978.7618   $978.76   $978.75   $978.60