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	$49.84	9.420%	$54.5349	$54.53	$54.55	$54.50
Purchase #2	$49.65	9.772%	$54.5018	$54.50	$54.50	$54.50
Purchase #3	$42.53	12.670%	$47.9186	$47.92	$47.90	$47.90
Purchase #4	$227.72	9.155%	$248.5678	$248.57	$248.55	$248.60
Purchase #5	$195.62	13.532%	$222.0913	$222.09	$222.10	$222.10
Purchase #6	$16.91	7.204%	$18.1282	$18.13	$18.15	$18.10
Purchase #7	$65.76	10.471%	$72.6457	$72.65	$72.65	$72.60
7 purchase totals =	$648.03		$718.3883	$718.39	$718.40	$718.30