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	$59.53	11.493%	$66.3718	$66.37	$66.35	$66.40
Purchase #2	$170.54	3.345%	$176.2446	$176.24	$176.25	$176.20
Purchase #3	$161.90	7.575%	$174.1639	$174.16	$174.15	$174.20
Purchase #4	$117.40	8.198%	$127.0245	$127.02	$127.00	$127.00
Purchase #5	$105.97	9.542%	$116.0817	$116.08	$116.10	$116.10
Purchase #6	$92.71	8.575%	$100.6599	$100.66	$100.65	$100.70
Purchase #7	$242.64	11.262%	$269.9661	$269.97	$269.95	$270.00
7 purchase totals =	$950.69		$1,030.5125	$1,030.50	$1,030.45	$1,030.60