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	$20.66	11.571%	$23.0506	$23.05	$23.05	$23.10
Purchase #2	$98.42	7.421%	$105.7237	$105.72	$105.70	$105.70
Purchase #3	$177.30	7.594%	$190.7642	$190.76	$190.75	$190.80
Purchase #4	$115.55	10.361%	$127.5221	$127.52	$127.50	$127.50
Purchase #5	$231.78	10.720%	$256.6268	$256.63	$256.65	$256.60
Purchase #6	$165.36	10.726%	$183.0965	$183.10	$183.10	$183.10
Purchase #7	$28.69	11.666%	$32.037	$32.04	$32.05	$32.00
7 purchase totals =	$837.76		$918.8209	$918.82	$918.80	$918.80