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	$24.45	12.383%	$27.4776	$27.48	$27.50	$27.50
Purchase #2	$78.58	3.860%	$81.6132	$81.61	$81.60	$81.60
Purchase #3	$114.89	11.122%	$127.6681	$127.67	$127.65	$127.70
Purchase #4	$77.79	4.270%	$81.1116	$81.11	$81.10	$81.10
Purchase #5	$105.41	6.600%	$112.3671	$112.37	$112.35	$112.40
Purchase #6	$154.49	12.231%	$173.3857	$173.39	$173.40	$173.40
Purchase #7	$180.75	7.789%	$194.8286	$194.83	$194.85	$194.80
7 purchase totals =	$736.36		$798.4519	$798.46	$798.45	$798.50