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	$78.78	12.147%	$88.3494	$88.35	$88.35	$88.30
Purchase #2	$127.42	7.742%	$137.2849	$137.28	$137.30	$137.30
Purchase #3	$226.47	11.583%	$252.702	$252.70	$252.70	$252.70
Purchase #4	$75.32	11.433%	$83.9313	$83.93	$83.95	$83.90
Purchase #5	$31.46	5.275%	$33.1195	$33.12	$33.10	$33.10
Purchase #6	$43.60	9.367%	$47.684	$47.68	$47.70	$47.70
Purchase #7	$111.87	10.431%	$123.5392	$123.54	$123.55	$123.50
7 purchase totals =	$694.92		$766.6103	$766.60	$766.65	$766.50