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	$18.38	13.314%	$20.8271	$20.83	$20.85	$20.80
Purchase #2	$241.38	10.258%	$266.1408	$266.14	$266.15	$266.10
Purchase #3	$137.49	13.398%	$155.9109	$155.91	$155.90	$155.90
Purchase #4	$160.84	13.391%	$182.3781	$182.38	$182.40	$182.40
Purchase #5	$9.66	11.276%	$10.7493	$10.75	$10.75	$10.70
Purchase #6	$123.49	5.325%	$130.0658	$130.07	$130.05	$130.10
Purchase #7	$155.28	4.497%	$162.2629	$162.26	$162.25	$162.30
7 purchase totals =	$846.52		$928.3349	$928.34	$928.35	$928.30