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	$106.47	4.556%	$111.3208	$111.32	$111.30	$111.30
Purchase #2	$145.40	8.725%	$158.0862	$158.09	$158.10	$158.10
Purchase #3	$156.47	12.728%	$176.3855	$176.39	$176.40	$176.40
Purchase #4	$127.30	13.750%	$144.8038	$144.80	$144.80	$144.80
Purchase #5	$227.43	12.165%	$255.0969	$255.10	$255.10	$255.10
Purchase #6	$245.99	13.180%	$278.4115	$278.41	$278.40	$278.40
Purchase #7	$158.75	11.673%	$177.2809	$177.28	$177.30	$177.30
7 purchase totals =	$1,167.81		$1,301.3856	$1,301.39	$1,301.40	$1,301.40