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	$123.38	3.586%	$127.8044	$127.80	$127.80	$127.80
Purchase #2	$244.44	13.830%	$278.2461	$278.25	$278.25	$278.20
Purchase #3	$177.59	5.354%	$187.0982	$187.10	$187.10	$187.10
Purchase #4	$105.90	10.514%	$117.0343	$117.03	$117.05	$117.00
Purchase #5	$83.70	8.431%	$90.7567	$90.76	$90.75	$90.80
Purchase #6	$201.25	12.491%	$226.3881	$226.39	$226.40	$226.40
Purchase #7	$55.68	6.862%	$59.5008	$59.50	$59.50	$59.50
7 purchase totals =	$991.94		$1,086.8286	$1,086.83	$1,086.85	$1,086.80