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	$10.49	10.491%	$11.5905	$11.59	$11.60	$11.60
Purchase #2	$71.78	10.260%	$79.1446	$79.14	$79.15	$79.10
Purchase #3	$138.76	3.860%	$144.1161	$144.12	$144.10	$144.10
Purchase #4	$180.46	6.743%	$192.6284	$192.63	$192.65	$192.60
Purchase #5	$238.29	7.395%	$255.9115	$255.91	$255.90	$255.90
Purchase #6	$142.52	10.104%	$156.9202	$156.92	$156.90	$156.90
Purchase #7	$78.44	4.457%	$81.9361	$81.94	$81.95	$81.90
7 purchase totals =	$860.74		$922.2474	$922.25	$922.25	$922.10