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	$115.90	10.112%	$127.6198	$127.62	$127.60	$127.60
Purchase #2	$178.75	3.791%	$185.5264	$185.53	$185.55	$185.50
Purchase #3	$108.58	8.637%	$117.9581	$117.96	$117.95	$118.00
Purchase #4	$21.49	13.834%	$24.4629	$24.46	$24.45	$24.50
Purchase #5	$12.63	9.502%	$13.8301	$13.83	$13.85	$13.80
Purchase #6	$18.33	6.131%	$19.4538	$19.45	$19.45	$19.50
Purchase #7	$166.90	3.794%	$173.2322	$173.23	$173.25	$173.20
7 purchase totals =	$622.58		$662.0833	$662.08	$662.10	$662.10