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	$101.55	12.801%	$114.5494	$114.55	$114.55	$114.50
Purchase #2	$150.92	3.679%	$156.4723	$156.47	$156.45	$156.50
Purchase #3	$179.62	4.828%	$188.2921	$188.29	$188.30	$188.30
Purchase #4	$10.72	8.545%	$11.636	$11.64	$11.65	$11.60
Purchase #5	$125.65	7.224%	$134.727	$134.73	$134.75	$134.70
Purchase #6	$64.76	9.178%	$70.7037	$70.70	$70.70	$70.70
Purchase #7	$89.81	11.536%	$100.1705	$100.17	$100.15	$100.20
7 purchase totals =	$723.03		$776.5510	$776.55	$776.55	$776.50