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	$99.94	8.866%	$108.8007	$108.80	$108.80	$108.80
Purchase #2	$119.33	10.745%	$132.152	$132.15	$132.15	$132.20
Purchase #3	$74.90	10.259%	$82.584	$82.58	$82.60	$82.60
Purchase #4	$142.85	10.787%	$158.2592	$158.26	$158.25	$158.30
Purchase #5	$119.84	6.567%	$127.7099	$127.71	$127.70	$127.70
Purchase #6	$231.90	9.678%	$254.3433	$254.34	$254.35	$254.30
Purchase #7	$24.26	11.313%	$27.0045	$27.00	$27.00	$27.00
7 purchase totals =	$813.02		$890.8536	$890.84	$890.85	$890.90