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	$20.77	3.247%	$21.4444	$21.44	$21.45	$21.40
Purchase #2	$115.49	10.698%	$127.8451	$127.85	$127.85	$127.80
Purchase #3	$122.66	5.838%	$129.8209	$129.82	$129.80	$129.80
Purchase #4	$99.88	10.776%	$110.6431	$110.64	$110.65	$110.60
Purchase #5	$18.33	5.788%	$19.3909	$19.39	$19.40	$19.40
Purchase #6	$83.25	3.579%	$86.2295	$86.23	$86.25	$86.20
Purchase #7	$116.91	12.373%	$131.3753	$131.38	$131.40	$131.40
7 purchase totals =	$577.29		$626.7492	$626.75	$626.80	$626.60