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	$103.86	12.477%	$116.8186	$116.82	$116.80	$116.80
Purchase #2	$117.54	8.735%	$127.8071	$127.81	$127.80	$127.80
Purchase #3	$62.33	5.358%	$65.6696	$65.67	$65.65	$65.70
Purchase #4	$91.46	10.752%	$101.2938	$101.29	$101.30	$101.30
Purchase #5	$231.79	3.309%	$239.4599	$239.46	$239.45	$239.50
Purchase #6	$178.71	6.229%	$189.8418	$189.84	$189.85	$189.80
Purchase #7	$202.69	13.517%	$230.0876	$230.09	$230.10	$230.10
7 purchase totals =	$988.38		$1,070.9784	$1,070.98	$1,070.95	$1,071.00