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	$10.40	4.354%	$10.8528	$10.85	$10.85	$10.90
Purchase #2	$132.52	12.145%	$148.6146	$148.61	$148.60	$148.60
Purchase #3	$59.42	5.578%	$62.7344	$62.73	$62.75	$62.70
Purchase #4	$172.64	8.380%	$187.1072	$187.11	$187.10	$187.10
Purchase #5	$67.96	6.635%	$72.4691	$72.47	$72.45	$72.50
Purchase #6	$66.56	13.269%	$75.3918	$75.39	$75.40	$75.40
Purchase #7	$81.83	12.133%	$91.7584	$91.76	$91.75	$91.80
7 purchase totals =	$591.33		$648.9283	$648.92	$648.90	$649.00