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	$90.25	11.760%	$100.8634	$100.86	$100.85	$100.90
Purchase #2	$172.51	3.219%	$178.0631	$178.06	$178.05	$178.10
Purchase #3	$29.52	4.561%	$30.8664	$30.87	$30.85	$30.90
Purchase #4	$30.78	11.817%	$34.4173	$34.42	$34.40	$34.40
Purchase #5	$199.56	11.706%	$222.9205	$222.92	$222.90	$222.90
Purchase #6	$112.76	8.477%	$122.3187	$122.32	$122.30	$122.30
Purchase #7	$235.94	12.799%	$266.138	$266.14	$266.15	$266.10
7 purchase totals =	$871.32		$955.5874	$955.59	$955.50	$955.60