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	$36.81	9.828%	$40.4277	$40.43	$40.45	$40.40
Purchase #2	$245.86	6.451%	$261.7204	$261.72	$261.70	$261.70
Purchase #3	$182.42	12.432%	$205.0985	$205.10	$205.10	$205.10
Purchase #4	$185.82	9.631%	$203.7163	$203.72	$203.70	$203.70
Purchase #5	$45.52	13.209%	$51.5327	$51.53	$51.55	$51.50
Purchase #6	$7.29	6.839%	$7.7886	$7.79	$7.80	$7.80
Purchase #7	$139.59	3.203%	$144.0611	$144.06	$144.05	$144.10
7 purchase totals =	$843.31		$914.3453	$914.35	$914.35	$914.30