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	$123.64	3.400%	$127.8438	$127.84	$127.85	$127.80
Purchase #2	$138.33	3.501%	$143.1729	$143.17	$143.15	$143.20
Purchase #3	$238.77	11.754%	$266.835	$266.84	$266.85	$266.80
Purchase #4	$10.54	3.286%	$10.8863	$10.89	$10.90	$10.90
Purchase #5	$130.54	10.522%	$144.2754	$144.28	$144.30	$144.30
Purchase #6	$17.59	4.832%	$18.4399	$18.44	$18.45	$18.40
Purchase #7	$179.66	6.793%	$191.8643	$191.86	$191.85	$191.90
7 purchase totals =	$839.07		$903.3176	$903.32	$903.35	$903.30