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 $175.64   4.788%   $184.0496   $184.05   $184.05   $184.00  
  Purchase #2 $231.77   13.278%   $262.5444   $262.54   $262.55   $262.50  
  Purchase #3 $199.96   11.265%   $222.4855   $222.49   $222.50   $222.50  
  Purchase #4 $207.25   9.586%   $227.117   $227.12   $227.10   $227.10  
  Purchase #5 $225.62   10.722%   $249.811   $249.81   $249.80   $249.80  
  Purchase #6 $149.79   4.832%   $157.0279   $157.03   $157.05   $157.00  
  Purchase #7 $35.93   6.839%   $38.3873   $38.39   $38.40   $38.40  
  7 purchase totals = $1,225.96       $1,341.4227   $1,341.43   $1,341.45   $1,341.30