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	$153.31	3.332%	$158.4183	$158.42	$158.40	$158.40
Purchase #2	$39.71	9.625%	$43.5321	$43.53	$43.55	$43.50
Purchase #3	$188.97	10.666%	$209.1255	$209.13	$209.15	$209.10
Purchase #4	$26.83	8.574%	$29.1304	$29.13	$29.15	$29.10
Purchase #5	$111.99	9.404%	$122.5215	$122.52	$122.50	$122.50
Purchase #6	$139.66	4.524%	$145.9782	$145.98	$146.00	$146.00
Purchase #7	$113.36	12.661%	$127.7125	$127.71	$127.70	$127.70
7 purchase totals =	$773.83		$836.4185	$836.42	$836.45	$836.30