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	$150.41	3.240%	$155.2833	$155.28	$155.30	$155.30
Purchase #2	$161.31	6.619%	$171.9871	$171.99	$172.00	$172.00
Purchase #3	$38.93	6.444%	$41.4386	$41.44	$41.45	$41.40
Purchase #4	$107.54	9.316%	$117.5584	$117.56	$117.55	$117.60
Purchase #5	$20.84	4.684%	$21.8161	$21.82	$21.80	$21.80
Purchase #6	$51.25	6.796%	$54.733	$54.73	$54.75	$54.70
Purchase #7	$53.73	3.163%	$55.4295	$55.43	$55.45	$55.40
7 purchase totals =	$584.01		$618.2460	$618.25	$618.30	$618.20