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	$66.60	5.213%	$70.0719	$70.07	$70.05	$70.10
Purchase #2	$67.52	10.735%	$74.7683	$74.77	$74.75	$74.80
Purchase #3	$17.90	13.473%	$20.3117	$20.31	$20.30	$20.30
Purchase #4	$127.43	13.849%	$145.0778	$145.08	$145.10	$145.10
Purchase #5	$220.51	6.361%	$234.5366	$234.54	$234.55	$234.50
Purchase #6	$68.39	13.271%	$77.466	$77.47	$77.45	$77.50
Purchase #7	$42.85	6.824%	$45.7741	$45.77	$45.75	$45.80
7 purchase totals =	$611.20		$668.0064	$668.01	$667.95	$668.10