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	$180.60	13.678%	$205.3025	$205.30	$205.30	$205.30
Purchase #2	$193.46	9.471%	$211.7826	$211.78	$211.80	$211.80
Purchase #3	$163.25	9.117%	$178.1335	$178.13	$178.15	$178.10
Purchase #4	$126.68	4.669%	$132.5947	$132.59	$132.60	$132.60
Purchase #5	$49.82	10.167%	$54.8852	$54.89	$54.90	$54.90
Purchase #6	$119.49	6.739%	$127.5424	$127.54	$127.55	$127.50
Purchase #7	$43.56	12.147%	$48.8512	$48.85	$48.85	$48.90
7 purchase totals =	$876.86		$959.0921	$959.08	$959.15	$959.10