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	$155.74	3.301%	$160.881	$160.88	$160.90	$160.90
Purchase #2	$75.45	4.585%	$78.9094	$78.91	$78.90	$78.90
Purchase #3	$21.93	12.871%	$24.7526	$24.75	$24.75	$24.80
Purchase #4	$7.72	11.147%	$8.5805	$8.58	$8.60	$8.60
Purchase #5	$139.82	10.243%	$154.1418	$154.14	$154.15	$154.10
Purchase #6	$172.33	10.140%	$189.8043	$189.80	$189.80	$189.80
Purchase #7	$244.30	12.333%	$274.4295	$274.43	$274.45	$274.40
7 purchase totals =	$817.29		$891.4991	$891.49	$891.55	$891.50