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	$46.73	7.598%	$50.2805	$50.28	$50.30	$50.30
Purchase #2	$82.49	9.232%	$90.1055	$90.11	$90.10	$90.10
Purchase #3	$95.86	8.153%	$103.6755	$103.68	$103.70	$103.70
Purchase #4	$51.97	8.371%	$56.3204	$56.32	$56.30	$56.30
Purchase #5	$230.80	10.746%	$255.6018	$255.60	$255.60	$255.60
Purchase #6	$111.73	12.812%	$126.0448	$126.04	$126.05	$126.00
Purchase #7	$146.27	12.629%	$164.7424	$164.74	$164.75	$164.70
7 purchase totals =	$765.85		$846.7709	$846.77	$846.80	$846.70