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	$35.88	10.454%	$39.6309	$39.63	$39.65	$39.60
Purchase #2	$52.50	3.842%	$54.5171	$54.52	$54.50	$54.50
Purchase #3	$47.93	7.719%	$51.6297	$51.63	$51.65	$51.60
Purchase #4	$137.92	5.688%	$145.7649	$145.76	$145.75	$145.80
Purchase #5	$146.91	4.437%	$153.4284	$153.43	$153.45	$153.40
Purchase #6	$27.61	12.769%	$31.1355	$31.14	$31.15	$31.10
Purchase #7	$102.93	8.121%	$111.2889	$111.29	$111.30	$111.30
7 purchase totals =	$551.68		$587.3954	$587.40	$587.45	$587.30