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	$164.91	4.166%	$171.7802	$171.78	$171.80	$171.80
Purchase #2	$91.69	8.240%	$99.2453	$99.25	$99.25	$99.20
Purchase #3	$39.36	10.753%	$43.5924	$43.59	$43.60	$43.60
Purchase #4	$204.93	8.743%	$222.847	$222.85	$222.85	$222.80
Purchase #5	$139.87	13.187%	$158.3147	$158.31	$158.30	$158.30
Purchase #6	$44.49	9.788%	$48.8447	$48.84	$48.85	$48.80
Purchase #7	$227.37	12.793%	$256.4574	$256.46	$256.45	$256.50
7 purchase totals =	$912.62		$1,001.0817	$1,001.08	$1,001.10	$1,001.00