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	$66.76	3.445%	$69.0599	$69.06	$69.05	$69.10
Purchase #2	$233.29	13.167%	$264.0073	$264.01	$264.00	$264.00
Purchase #3	$138.76	3.654%	$143.8303	$143.83	$143.85	$143.80
Purchase #4	$90.65	9.549%	$99.3062	$99.31	$99.30	$99.30
Purchase #5	$32.37	4.789%	$33.9202	$33.92	$33.90	$33.90
Purchase #6	$48.56	11.187%	$53.9924	$53.99	$54.00	$54.00
Purchase #7	$145.66	8.688%	$158.3149	$158.31	$158.30	$158.30
7 purchase totals =	$756.05		$822.4312	$822.43	$822.40	$822.40