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 $50.95   5.545%   $53.7752   $53.78   $53.80   $53.80  
  Purchase #2 $164.91   10.632%   $182.4432   $182.44   $182.45   $182.40  
  Purchase #3 $195.90   6.496%   $208.6257   $208.63   $208.65   $208.60  
  Purchase #4 $37.73   3.414%   $39.0181   $39.02   $39.00   $39.00  
  Purchase #5 $98.61   5.496%   $104.0296   $104.03   $104.05   $104.00  
  Purchase #6 $196.58   10.664%   $217.5433   $217.54   $217.55   $217.50  
  Purchase #7 $189.60   12.868%   $213.9977   $214.00   $214.00   $214.00  
  7 purchase totals = $934.28       $1,019.4328   $1,019.44   $1,019.50   $1,019.30