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	$240.42	6.304%	$255.5761	$255.58	$255.60	$255.60
Purchase #2	$37.28	5.596%	$39.3662	$39.37	$39.35	$39.40
Purchase #3	$127.62	4.508%	$133.3731	$133.37	$133.35	$133.40
Purchase #4	$218.44	5.753%	$231.0069	$231.01	$231.00	$231.00
Purchase #5	$159.93	4.284%	$166.7814	$166.78	$166.80	$166.80
Purchase #6	$137.71	5.393%	$145.1367	$145.14	$145.15	$145.10
Purchase #7	$165.68	8.124%	$179.1398	$179.14	$179.15	$179.10
7 purchase totals =	$1,087.08		$1,150.3802	$1,150.39	$1,150.40	$1,150.40