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	$152.56	13.677%	$173.4256	$173.43	$173.45	$173.40
Purchase #2	$250.60	13.524%	$284.4911	$284.49	$284.50	$284.50
Purchase #3	$78.27	10.137%	$86.2042	$86.20	$86.20	$86.20
Purchase #4	$31.40	4.387%	$32.7775	$32.78	$32.80	$32.80
Purchase #5	$14.53	5.398%	$15.3143	$15.31	$15.30	$15.30
Purchase #6	$111.71	8.178%	$120.8456	$120.85	$120.85	$120.80
Purchase #7	$130.51	11.854%	$145.9807	$145.98	$146.00	$146.00
7 purchase totals =	$769.58		$859.0390	$859.04	$859.10	$859.00