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	$29.64	7.463%	$31.852	$31.85	$31.85	$31.90
Purchase #2	$244.55	13.483%	$277.5227	$277.52	$277.50	$277.50
Purchase #3	$97.67	7.660%	$105.1515	$105.15	$105.15	$105.20
Purchase #4	$171.83	7.689%	$185.042	$185.04	$185.05	$185.00
Purchase #5	$155.39	3.166%	$160.3096	$160.31	$160.30	$160.30
Purchase #6	$61.25	6.823%	$65.4291	$65.43	$65.45	$65.40
Purchase #7	$104.70	11.828%	$117.0839	$117.08	$117.10	$117.10
7 purchase totals =	$865.03		$942.3908	$942.38	$942.40	$942.40