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	$228.91	9.559%	$250.7915	$250.79	$250.80	$250.80
Purchase #2	$109.34	12.685%	$123.2098	$123.21	$123.20	$123.20
Purchase #3	$102.52	5.511%	$108.1699	$108.17	$108.15	$108.20
Purchase #4	$95.92	7.735%	$103.3394	$103.34	$103.35	$103.30
Purchase #5	$145.78	8.787%	$158.5897	$158.59	$158.60	$158.60
Purchase #6	$88.40	8.263%	$95.7045	$95.70	$95.70	$95.70
Purchase #7	$105.81	3.608%	$109.6276	$109.63	$109.65	$109.60
7 purchase totals =	$876.68		$949.4324	$949.43	$949.45	$949.40