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	$244.80	4.321%	$255.3778	$255.38	$255.40	$255.40
Purchase #2	$234.61	12.481%	$263.8917	$263.89	$263.90	$263.90
Purchase #3	$138.59	4.651%	$145.0358	$145.04	$145.05	$145.00
Purchase #4	$147.92	4.839%	$155.0778	$155.08	$155.10	$155.10
Purchase #5	$209.50	10.178%	$230.8229	$230.82	$230.80	$230.80
Purchase #6	$97.99	13.642%	$111.3578	$111.36	$111.35	$111.40
Purchase #7	$198.32	13.579%	$225.2499	$225.25	$225.25	$225.20
7 purchase totals =	$1,271.73		$1,386.8137	$1,386.82	$1,386.85	$1,386.80