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	$123.45	11.267%	$137.3591	$137.36	$137.35	$137.40
Purchase #2	$245.46	5.261%	$258.3737	$258.37	$258.35	$258.40
Purchase #3	$37.26	13.178%	$42.1701	$42.17	$42.15	$42.20
Purchase #4	$15.37	11.397%	$17.1217	$17.12	$17.10	$17.10
Purchase #5	$38.54	10.758%	$42.6861	$42.69	$42.70	$42.70
Purchase #6	$128.52	13.277%	$145.5836	$145.58	$145.60	$145.60
Purchase #7	$52.51	3.248%	$54.2155	$54.22	$54.20	$54.20
7 purchase totals =	$641.11		$697.5098	$697.51	$697.45	$697.60