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	$167.30	5.428%	$176.381	$176.38	$176.40	$176.40
Purchase #2	$128.34	12.520%	$144.4082	$144.41	$144.40	$144.40
Purchase #3	$138.71	5.871%	$146.8537	$146.85	$146.85	$146.90
Purchase #4	$160.83	7.836%	$173.4326	$173.43	$173.45	$173.40
Purchase #5	$240.56	10.475%	$265.7587	$265.76	$265.75	$265.80
Purchase #6	$51.42	13.286%	$58.2517	$58.25	$58.25	$58.30
Purchase #7	$195.78	10.217%	$215.7828	$215.78	$215.80	$215.80
7 purchase totals =	$1,082.94		$1,180.8687	$1,180.86	$1,180.90	$1,181.00