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	$106.83	4.359%	$111.4867	$111.49	$111.50	$111.50
Purchase #2	$42.33	9.205%	$46.2265	$46.23	$46.25	$46.20
Purchase #3	$95.99	8.299%	$103.9562	$103.96	$103.95	$104.00
Purchase #4	$145.73	13.384%	$165.2345	$165.23	$165.25	$165.20
Purchase #5	$173.27	6.828%	$185.1009	$185.10	$185.10	$185.10
Purchase #6	$91.46	13.202%	$103.5345	$103.53	$103.55	$103.50
Purchase #7	$25.66	5.584%	$27.0929	$27.09	$27.10	$27.10
7 purchase totals =	$681.27		$742.6322	$742.63	$742.70	$742.60