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	$22.77	5.382%	$23.9955	$24.00	$24.00	$24.00
Purchase #2	$47.95	11.278%	$53.3578	$53.36	$53.35	$53.40
Purchase #3	$222.92	4.623%	$233.2256	$233.23	$233.25	$233.20
Purchase #4	$19.76	3.385%	$20.4289	$20.43	$20.45	$20.40
Purchase #5	$45.83	4.872%	$48.0628	$48.06	$48.05	$48.10
Purchase #6	$228.75	5.574%	$241.5005	$241.50	$241.50	$241.50
Purchase #7	$122.40	13.824%	$139.3206	$139.32	$139.30	$139.30
7 purchase totals =	$710.38		$759.8917	$759.90	$759.90	$759.90