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	$245.99	10.223%	$271.1376	$271.14	$271.15	$271.10
Purchase #2	$78.51	12.670%	$88.4572	$88.46	$88.45	$88.50
Purchase #3	$77.74	10.105%	$85.5956	$85.60	$85.60	$85.60
Purchase #4	$129.84	9.839%	$142.615	$142.62	$142.60	$142.60
Purchase #5	$115.65	9.353%	$126.4667	$126.47	$126.45	$126.50
Purchase #6	$158.25	9.510%	$173.2996	$173.30	$173.30	$173.30
Purchase #7	$86.98	6.129%	$92.311	$92.31	$92.30	$92.30
7 purchase totals =	$892.96		$979.8827	$979.90	$979.85	$979.90