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	$131.90	7.177%	$141.3665	$141.37	$141.35	$141.40
Purchase #2	$214.41	11.297%	$238.6319	$238.63	$238.65	$238.60
Purchase #3	$111.90	10.710%	$123.8845	$123.88	$123.90	$123.90
Purchase #4	$70.52	6.231%	$74.9141	$74.91	$74.90	$74.90
Purchase #5	$40.80	10.420%	$45.0514	$45.05	$45.05	$45.10
Purchase #6	$46.46	10.147%	$51.1743	$51.17	$51.15	$51.20
Purchase #7	$172.47	11.508%	$192.3178	$192.32	$192.30	$192.30
7 purchase totals =	$788.46		$867.3405	$867.33	$867.30	$867.40