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 $111.47   4.190%   $116.1406   $116.14   $116.15   $116.10  
  Purchase #2 $115.42   6.344%   $122.7422   $122.74   $122.75   $122.70  
  Purchase #3 $184.25   4.676%   $192.8655   $192.87   $192.85   $192.90  
  Purchase #4 $99.44   8.544%   $107.9362   $107.94   $107.95   $107.90  
  Purchase #5 $190.53   9.580%   $208.7828   $208.78   $208.80   $208.80  
  Purchase #6 $143.61   10.389%   $158.5296   $158.53   $158.55   $158.50  
  Purchase #7 $119.36   11.222%   $132.7546   $132.75   $132.75   $132.80  
  7 purchase totals = $964.08       $1,039.7515   $1,039.75   $1,039.80   $1,039.70