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	$90.89	10.462%	$100.3989	$100.40	$100.40	$100.40
Purchase #2	$108.67	13.687%	$123.5437	$123.54	$123.55	$123.50
Purchase #3	$161.84	6.247%	$171.9501	$171.95	$171.95	$172.00
Purchase #4	$118.66	5.495%	$125.1804	$125.18	$125.20	$125.20
Purchase #5	$146.38	3.824%	$151.9776	$151.98	$152.00	$152.00
Purchase #6	$22.28	8.166%	$24.0994	$24.10	$24.10	$24.10
Purchase #7	$214.64	13.398%	$243.3975	$243.40	$243.40	$243.40
7 purchase totals =	$863.36		$940.5476	$940.55	$940.60	$940.60