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 $199.42   7.636%   $214.6477   $214.65   $214.65   $214.60  
  Purchase #2 $239.73   11.477%   $267.2438   $267.24   $267.25   $267.20  
  Purchase #3 $119.41   5.442%   $125.9083   $125.91   $125.90   $125.90  
  Purchase #4 $245.34   6.275%   $260.7351   $260.74   $260.75   $260.70  
  Purchase #5 $224.75   9.567%   $246.2518   $246.25   $246.25   $246.30  
  Purchase #6 $12.48   13.559%   $14.1722   $14.17   $14.15   $14.20  
  Purchase #7 $164.60   10.763%   $182.3159   $182.32   $182.30   $182.30  
  7 purchase totals = $1,205.73       $1,311.2748   $1,311.28   $1,311.25   $1,311.20