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	$102.87	6.265%	$109.3148	$109.31	$109.30	$109.30
Purchase #2	$60.59	5.389%	$63.8552	$63.86	$63.85	$63.90
Purchase #3	$178.44	12.563%	$200.8574	$200.86	$200.85	$200.90
Purchase #4	$83.77	10.338%	$92.4301	$92.43	$92.45	$92.40
Purchase #5	$127.29	5.832%	$134.7136	$134.71	$134.70	$134.70
Purchase #6	$145.56	4.469%	$152.0651	$152.07	$152.05	$152.10
Purchase #7	$244.49	8.832%	$266.0834	$266.08	$266.10	$266.10
7 purchase totals =	$943.01		$1,019.3196	$1,019.32	$1,019.30	$1,019.40