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	$37.93	5.568%	$40.0419	$40.04	$40.05	$40.00
Purchase #2	$67.86	13.715%	$77.167	$77.17	$77.15	$77.20
Purchase #3	$50.33	6.851%	$53.7781	$53.78	$53.80	$53.80
Purchase #4	$41.30	4.517%	$43.1655	$43.17	$43.15	$43.20
Purchase #5	$21.82	9.274%	$23.8436	$23.84	$23.85	$23.80
Purchase #6	$158.98	9.325%	$173.8049	$173.80	$173.80	$173.80
Purchase #7	$62.47	6.405%	$66.4712	$66.47	$66.45	$66.50
7 purchase totals =	$440.69		$478.2722	$478.27	$478.25	$478.30