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	$111.80	13.859%	$127.2944	$127.29	$127.30	$127.30
Purchase #2	$57.75	4.318%	$60.2436	$60.24	$60.25	$60.20
Purchase #3	$236.92	6.243%	$251.7109	$251.71	$251.70	$251.70
Purchase #4	$210.68	6.244%	$223.8349	$223.83	$223.85	$223.80
Purchase #5	$86.45	13.627%	$98.2305	$98.23	$98.25	$98.20
Purchase #6	$84.50	3.388%	$87.3629	$87.36	$87.35	$87.40
Purchase #7	$100.78	10.728%	$111.5917	$111.59	$111.60	$111.60
7 purchase totals =	$888.88		$960.2689	$960.25	$960.30	$960.20