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	$54.61	3.607%	$56.5798	$56.58	$56.60	$56.60
Purchase #2	$230.78	11.266%	$256.7797	$256.78	$256.80	$256.80
Purchase #3	$194.71	13.301%	$220.6084	$220.61	$220.60	$220.60
Purchase #4	$39.39	7.594%	$42.3813	$42.38	$42.40	$42.40
Purchase #5	$153.84	11.592%	$171.6731	$171.67	$171.65	$171.70
Purchase #6	$247.58	9.762%	$271.7488	$271.75	$271.75	$271.70
Purchase #7	$154.48	8.321%	$167.3343	$167.33	$167.35	$167.30
7 purchase totals =	$1,075.39		$1,187.1054	$1,187.10	$1,187.15	$1,187.10