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	$27.79	7.125%	$29.77	$29.77	$29.75	$29.80
Purchase #2	$179.64	4.847%	$188.3472	$188.35	$188.35	$188.30
Purchase #3	$99.50	9.863%	$109.3137	$109.31	$109.30	$109.30
Purchase #4	$37.64	7.840%	$40.591	$40.59	$40.60	$40.60
Purchase #5	$146.80	7.736%	$158.1564	$158.16	$158.15	$158.20
Purchase #6	$73.98	4.409%	$77.2418	$77.24	$77.25	$77.20
Purchase #7	$72.40	10.631%	$80.0968	$80.10	$80.10	$80.10
7 purchase totals =	$637.75		$683.5169	$683.52	$683.50	$683.50