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	$90.49	11.461%	$100.8611	$100.86	$100.85	$100.90
Purchase #2	$29.25	12.630%	$32.9443	$32.94	$32.95	$32.90
Purchase #3	$167.91	5.585%	$177.2878	$177.29	$177.30	$177.30
Purchase #4	$170.39	8.232%	$184.4165	$184.42	$184.40	$184.40
Purchase #5	$117.94	4.457%	$123.1966	$123.20	$123.20	$123.20
Purchase #6	$40.72	10.542%	$45.0127	$45.01	$45.00	$45.00
Purchase #7	$67.72	3.478%	$70.0753	$70.08	$70.10	$70.10
7 purchase totals =	$684.42		$733.7943	$733.80	$733.80	$733.80