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	$172.42	7.343%	$185.0808	$185.08	$185.10	$185.10
Purchase #2	$188.65	5.526%	$199.0748	$199.07	$199.05	$199.10
Purchase #3	$178.59	9.470%	$195.5025	$195.50	$195.50	$195.50
Purchase #4	$77.82	9.344%	$85.0915	$85.09	$85.10	$85.10
Purchase #5	$19.60	4.353%	$20.4532	$20.45	$20.45	$20.50
Purchase #6	$90.30	8.828%	$98.2717	$98.27	$98.25	$98.30
Purchase #7	$41.93	11.222%	$46.6354	$46.64	$46.65	$46.60
7 purchase totals =	$769.31		$830.1099	$830.10	$830.10	$830.20