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	$16.93	3.433%	$17.5112	$17.51	$17.50	$17.50
Purchase #2	$234.28	4.354%	$244.4806	$244.48	$244.50	$244.50
Purchase #3	$158.92	9.479%	$173.984	$173.98	$174.00	$174.00
Purchase #4	$146.84	7.812%	$158.3111	$158.31	$158.30	$158.30
Purchase #5	$118.78	5.175%	$124.9269	$124.93	$124.95	$124.90
Purchase #6	$82.45	4.406%	$86.0827	$86.08	$86.10	$86.10
Purchase #7	$242.56	3.163%	$250.2322	$250.23	$250.25	$250.20
7 purchase totals =	$1,000.76		$1,055.5287	$1,055.52	$1,055.60	$1,055.50