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	$127.45	9.345%	$139.3602	$139.36	$139.35	$139.40
Purchase #2	$89.80	12.403%	$100.9379	$100.94	$100.95	$100.90
Purchase #3	$20.45	9.693%	$22.4322	$22.43	$22.45	$22.40
Purchase #4	$206.43	10.595%	$228.3013	$228.30	$228.30	$228.30
Purchase #5	$116.64	10.822%	$129.2628	$129.26	$129.25	$129.30
Purchase #6	$164.60	4.575%	$172.1305	$172.13	$172.15	$172.10
Purchase #7	$183.84	13.355%	$208.3918	$208.39	$208.40	$208.40
7 purchase totals =	$909.21		$1,000.8167	$1,000.81	$1,000.85	$1,000.80