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	$34.61	11.195%	$38.4846	$38.48	$38.50	$38.50
Purchase #2	$162.49	3.198%	$167.6864	$167.69	$167.70	$167.70
Purchase #3	$105.30	9.625%	$115.4351	$115.44	$115.45	$115.40
Purchase #4	$22.39	11.251%	$24.9091	$24.91	$24.90	$24.90
Purchase #5	$11.86	4.330%	$12.3735	$12.37	$12.35	$12.40
Purchase #6	$103.42	7.494%	$111.1703	$111.17	$111.15	$111.20
Purchase #7	$35.75	11.701%	$39.9331	$39.93	$39.95	$39.90
7 purchase totals =	$475.82		$509.9921	$509.99	$510.00	$510.00