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	$41.52	9.305%	$45.3834	$45.38	$45.40	$45.40
Purchase #2	$145.94	3.681%	$151.3121	$151.31	$151.30	$151.30
Purchase #3	$46.72	4.397%	$48.7743	$48.77	$48.75	$48.80
Purchase #4	$62.89	5.531%	$66.3684	$66.37	$66.35	$66.40
Purchase #5	$38.56	5.139%	$40.5416	$40.54	$40.55	$40.50
Purchase #6	$6.96	13.727%	$7.9154	$7.92	$7.90	$7.90
Purchase #7	$174.60	5.451%	$184.1174	$184.12	$184.10	$184.10
7 purchase totals =	$517.19		$544.4126	$544.41	$544.35	$544.40