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	$57.70	3.106%	$59.4922	$59.49	$59.50	$59.50
Purchase #2	$149.81	11.525%	$167.0756	$167.08	$167.10	$167.10
Purchase #3	$116.91	8.642%	$127.0134	$127.01	$127.00	$127.00
Purchase #4	$52.87	11.355%	$58.8734	$58.87	$58.85	$58.90
Purchase #5	$210.99	9.408%	$230.8399	$230.84	$230.85	$230.80
Purchase #6	$20.55	5.302%	$21.6396	$21.64	$21.65	$21.60
Purchase #7	$103.61	11.532%	$115.5583	$115.56	$115.55	$115.60
7 purchase totals =	$712.44		$780.4924	$780.49	$780.50	$780.50