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	$100.79	8.173%	$109.0276	$109.03	$109.05	$109.00
Purchase #2	$75.27	13.859%	$85.7017	$85.70	$85.70	$85.70
Purchase #3	$41.50	5.498%	$43.7817	$43.78	$43.80	$43.80
Purchase #4	$232.88	10.447%	$257.209	$257.21	$257.20	$257.20
Purchase #5	$221.46	7.670%	$238.446	$238.45	$238.45	$238.40
Purchase #6	$245.75	5.343%	$258.8804	$258.88	$258.90	$258.90
Purchase #7	$148.75	6.733%	$158.7653	$158.77	$158.75	$158.80
7 purchase totals =	$1,066.40		$1,151.8117	$1,151.82	$1,151.85	$1,151.80