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	$9.76	13.820%	$11.1088	$11.11	$11.10	$11.10
Purchase #2	$101.77	3.563%	$105.3961	$105.40	$105.40	$105.40
Purchase #3	$199.39	8.533%	$216.4039	$216.40	$216.40	$216.40
Purchase #4	$95.27	4.723%	$99.7696	$99.77	$99.75	$99.80
Purchase #5	$17.82	11.819%	$19.9261	$19.93	$19.95	$19.90
Purchase #6	$109.47	5.209%	$115.1723	$115.17	$115.15	$115.20
Purchase #7	$91.82	9.288%	$100.3482	$100.35	$100.35	$100.30
7 purchase totals =	$625.30		$668.1250	$668.13	$668.10	$668.10