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	$155.56	9.618%	$170.5218	$170.52	$170.50	$170.50
Purchase #2	$200.51	12.865%	$226.3056	$226.31	$226.30	$226.30
Purchase #3	$145.61	8.588%	$158.115	$158.12	$158.10	$158.10
Purchase #4	$104.30	7.317%	$111.9316	$111.93	$111.95	$111.90
Purchase #5	$109.94	10.490%	$121.4727	$121.47	$121.45	$121.50
Purchase #6	$19.47	8.180%	$21.0626	$21.06	$21.05	$21.10
Purchase #7	$52.39	5.595%	$55.3212	$55.32	$55.30	$55.30
7 purchase totals =	$787.78		$864.7305	$864.73	$864.65	$864.70