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	$15.46	6.232%	$16.4235	$16.42	$16.40	$16.40
Purchase #2	$43.50	11.440%	$48.4764	$48.48	$48.50	$48.50
Purchase #3	$63.61	13.308%	$72.0752	$72.08	$72.10	$72.10
Purchase #4	$244.76	11.382%	$272.6186	$272.62	$272.60	$272.60
Purchase #5	$92.32	4.502%	$96.4762	$96.48	$96.50	$96.50
Purchase #6	$190.87	11.790%	$213.3736	$213.37	$213.35	$213.40
Purchase #7	$39.75	9.163%	$43.3923	$43.39	$43.40	$43.40
7 purchase totals =	$690.27		$762.8358	$762.84	$762.85	$762.90