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	$120.75	5.544%	$127.4444	$127.44	$127.45	$127.40
Purchase #2	$84.92	13.742%	$96.5897	$96.59	$96.60	$96.60
Purchase #3	$108.78	4.110%	$113.2509	$113.25	$113.25	$113.30
Purchase #4	$142.29	8.585%	$154.5056	$154.51	$154.50	$154.50
Purchase #5	$81.79	9.746%	$89.7613	$89.76	$89.75	$89.80
Purchase #6	$163.77	7.329%	$175.7727	$175.77	$175.75	$175.80
Purchase #7	$105.51	5.404%	$111.2118	$111.21	$111.20	$111.20
7 purchase totals =	$807.81		$868.5364	$868.53	$868.50	$868.60