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	$136.60	7.260%	$146.5172	$146.52	$146.50	$146.50
Purchase #2	$43.45	12.543%	$48.8999	$48.90	$48.90	$48.90
Purchase #3	$42.41	10.757%	$46.972	$46.97	$46.95	$47.00
Purchase #4	$105.57	8.264%	$114.2943	$114.29	$114.30	$114.30
Purchase #5	$116.88	9.351%	$127.8094	$127.81	$127.80	$127.80
Purchase #6	$250.91	5.715%	$265.2495	$265.25	$265.25	$265.20
Purchase #7	$107.37	4.258%	$111.9418	$111.94	$111.95	$111.90
7 purchase totals =	$803.19		$861.6841	$861.68	$861.65	$861.60