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	$45.82	13.210%	$51.8728	$51.87	$51.85	$51.90
Purchase #2	$81.88	10.819%	$90.7386	$90.74	$90.75	$90.70
Purchase #3	$100.26	12.543%	$112.8356	$112.84	$112.85	$112.80
Purchase #4	$249.42	8.747%	$271.2368	$271.24	$271.25	$271.20
Purchase #5	$112.88	4.818%	$118.3186	$118.32	$118.30	$118.30
Purchase #6	$71.83	8.694%	$78.0749	$78.07	$78.05	$78.10
Purchase #7	$212.50	10.868%	$235.5945	$235.59	$235.60	$235.60
7 purchase totals =	$874.59		$958.6718	$958.67	$958.65	$958.60