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	$120.83	8.623%	$131.2492	$131.25	$131.25	$131.20
Purchase #2	$158.75	8.469%	$172.1945	$172.19	$172.20	$172.20
Purchase #3	$97.50	7.757%	$105.0631	$105.06	$105.05	$105.10
Purchase #4	$146.43	6.604%	$156.1002	$156.10	$156.10	$156.10
Purchase #5	$136.43	3.195%	$140.7889	$140.79	$140.80	$140.80
Purchase #6	$111.72	10.715%	$123.6908	$123.69	$123.70	$123.70
Purchase #7	$141.87	5.416%	$149.5537	$149.55	$149.55	$149.60
7 purchase totals =	$913.53		$978.6404	$978.63	$978.65	$978.70