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	$194.31	11.755%	$217.1511	$217.15	$217.15	$217.20
Purchase #2	$148.59	9.482%	$162.6793	$162.68	$162.70	$162.70
Purchase #3	$97.92	6.766%	$104.5453	$104.55	$104.55	$104.50
Purchase #4	$71.45	11.822%	$79.8968	$79.90	$79.90	$79.90
Purchase #5	$39.87	9.339%	$43.5935	$43.59	$43.60	$43.60
Purchase #6	$216.26	5.607%	$228.3857	$228.39	$228.40	$228.40
Purchase #7	$129.42	12.526%	$145.6311	$145.63	$145.65	$145.60
7 purchase totals =	$897.82		$981.8828	$981.89	$981.95	$981.90