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	$107.87	11.766%	$120.562	$120.56	$120.55	$120.60
Purchase #2	$105.27	5.491%	$111.0504	$111.05	$111.05	$111.10
Purchase #3	$104.86	6.648%	$111.8311	$111.83	$111.85	$111.80
Purchase #4	$16.38	11.831%	$18.3179	$18.32	$18.30	$18.30
Purchase #5	$175.40	9.513%	$192.0858	$192.09	$192.10	$192.10
Purchase #6	$177.83	3.116%	$183.3712	$183.37	$183.35	$183.40
Purchase #7	$229.34	7.157%	$245.7539	$245.75	$245.75	$245.80
7 purchase totals =	$916.95		$982.9723	$982.97	$982.95	$983.10