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	$32.25	9.121%	$35.1915	$35.19	$35.20	$35.20
Purchase #2	$76.72	7.126%	$82.1871	$82.19	$82.20	$82.20
Purchase #3	$81.86	9.359%	$89.5213	$89.52	$89.50	$89.50
Purchase #4	$236.55	6.381%	$251.6443	$251.64	$251.65	$251.60
Purchase #5	$15.66	11.543%	$17.4676	$17.47	$17.45	$17.50
Purchase #6	$11.98	10.327%	$13.2172	$13.22	$13.20	$13.20
Purchase #7	$28.99	12.662%	$32.6607	$32.66	$32.65	$32.70
7 purchase totals =	$484.01		$521.8897	$521.89	$521.85	$521.90