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	$39.76	10.345%	$43.8732	$43.87	$43.85	$43.90
Purchase #2	$125.56	4.664%	$131.4161	$131.42	$131.40	$131.40
Purchase #3	$132.29	13.728%	$150.4508	$150.45	$150.45	$150.50
Purchase #4	$185.74	13.845%	$211.4557	$211.46	$211.45	$211.50
Purchase #5	$63.41	10.520%	$70.0807	$70.08	$70.10	$70.10
Purchase #6	$73.99	7.569%	$79.5903	$79.59	$79.60	$79.60
Purchase #7	$227.34	6.631%	$242.4149	$242.41	$242.40	$242.40
7 purchase totals =	$848.09		$929.2817	$929.28	$929.25	$929.40