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	$175.87	7.339%	$188.7771	$188.78	$188.80	$188.80
Purchase #2	$140.67	5.458%	$148.3478	$148.35	$148.35	$148.30
Purchase #3	$242.95	6.641%	$259.0843	$259.08	$259.10	$259.10
Purchase #4	$77.84	9.732%	$85.4154	$85.42	$85.40	$85.40
Purchase #5	$49.59	10.592%	$54.8426	$54.84	$54.85	$54.80
Purchase #6	$29.92	9.537%	$32.7735	$32.77	$32.75	$32.80
Purchase #7	$121.66	4.549%	$127.1943	$127.19	$127.20	$127.20
7 purchase totals =	$838.50		$896.4350	$896.43	$896.45	$896.40