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	$42.32	11.381%	$47.1364	$47.14	$47.15	$47.10
Purchase #2	$203.83	10.149%	$224.5167	$224.52	$224.50	$224.50
Purchase #3	$123.60	8.786%	$134.4595	$134.46	$134.45	$134.50
Purchase #4	$142.45	7.728%	$153.4585	$153.46	$153.45	$153.50
Purchase #5	$28.85	9.194%	$31.5025	$31.50	$31.50	$31.50
Purchase #6	$142.84	9.268%	$156.0784	$156.08	$156.10	$156.10
Purchase #7	$26.64	10.685%	$29.4865	$29.49	$29.50	$29.50
7 purchase totals =	$710.53		$776.6385	$776.65	$776.65	$776.70