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	$15.92	9.254%	$17.3932	$17.39	$17.40	$17.40
Purchase #2	$222.45	12.839%	$251.0104	$251.01	$251.00	$251.00
Purchase #3	$14.76	7.156%	$15.8162	$15.82	$15.80	$15.80
Purchase #4	$149.35	10.568%	$165.1333	$165.13	$165.15	$165.10
Purchase #5	$31.78	5.415%	$33.5009	$33.50	$33.50	$33.50
Purchase #6	$226.87	5.836%	$240.1101	$240.11	$240.10	$240.10
Purchase #7	$209.37	6.162%	$222.2714	$222.27	$222.25	$222.30
7 purchase totals =	$870.50		$945.2355	$945.23	$945.20	$945.20