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	$104.87	5.194%	$110.3169	$110.32	$110.30	$110.30
Purchase #2	$106.64	4.735%	$111.6894	$111.69	$111.70	$111.70
Purchase #3	$132.42	7.538%	$142.4018	$142.40	$142.40	$142.40
Purchase #4	$143.83	4.288%	$149.9974	$150.00	$150.00	$150.00
Purchase #5	$19.33	4.657%	$20.2302	$20.23	$20.25	$20.20
Purchase #6	$111.63	12.559%	$125.6496	$125.65	$125.65	$125.60
Purchase #7	$130.87	7.353%	$140.4929	$140.49	$140.50	$140.50
7 purchase totals =	$749.59		$800.7782	$800.78	$800.80	$800.70