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	$227.80	13.650%	$258.8947	$258.89	$258.90	$258.90
Purchase #2	$37.42	13.259%	$42.3815	$42.38	$42.40	$42.40
Purchase #3	$225.89	5.416%	$238.1242	$238.12	$238.10	$238.10
Purchase #4	$217.75	10.323%	$240.2283	$240.23	$240.25	$240.20
Purchase #5	$177.67	9.165%	$193.9535	$193.95	$193.95	$194.00
Purchase #6	$54.65	5.382%	$57.5913	$57.59	$57.60	$57.60
Purchase #7	$132.76	11.223%	$147.6597	$147.66	$147.65	$147.70
7 purchase totals =	$1,073.94		$1,178.8332	$1,178.82	$1,178.85	$1,178.90