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	$155.46	7.104%	$166.5039	$166.50	$166.50	$166.50
Purchase #2	$123.89	3.114%	$127.7479	$127.75	$127.75	$127.70
Purchase #3	$61.39	8.597%	$66.6677	$66.67	$66.65	$66.70
Purchase #4	$176.84	6.456%	$188.2568	$188.26	$188.25	$188.30
Purchase #5	$141.83	7.131%	$151.9439	$151.94	$151.95	$151.90
Purchase #6	$243.89	3.660%	$252.8164	$252.82	$252.80	$252.80
Purchase #7	$215.38	9.372%	$235.5654	$235.57	$235.55	$235.60
7 purchase totals =	$1,118.68		$1,189.5020	$1,189.51	$1,189.45	$1,189.50