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	$39.54	8.202%	$42.7831	$42.78	$42.80	$42.80
Purchase #2	$49.88	11.839%	$55.7853	$55.79	$55.80	$55.80
Purchase #3	$50.31	11.705%	$56.1988	$56.20	$56.20	$56.20
Purchase #4	$110.58	7.184%	$118.5241	$118.52	$118.50	$118.50
Purchase #5	$107.35	6.540%	$114.3707	$114.37	$114.35	$114.40
Purchase #6	$28.94	13.495%	$32.8455	$32.85	$32.85	$32.80
Purchase #7	$17.51	12.747%	$19.742	$19.74	$19.75	$19.70
7 purchase totals =	$404.11		$440.2495	$440.25	$440.25	$440.20