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	$30.43	6.852%	$32.5151	$32.52	$32.50	$32.50
Purchase #2	$9.82	8.404%	$10.6453	$10.65	$10.65	$10.60
Purchase #3	$97.56	12.720%	$109.9696	$109.97	$109.95	$110.00
Purchase #4	$99.32	9.752%	$109.0057	$109.01	$109.00	$109.00
Purchase #5	$5.31	5.758%	$5.6157	$5.62	$5.60	$5.60
Purchase #6	$45.29	5.660%	$47.8534	$47.85	$47.85	$47.90
Purchase #7	$190.28	10.135%	$209.5649	$209.56	$209.55	$209.60
7 purchase totals =	$478.01		$525.1697	$525.18	$525.10	$525.20