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	$247.50	12.823%	$279.2369	$279.24	$279.25	$279.20
Purchase #2	$38.95	3.664%	$40.3771	$40.38	$40.40	$40.40
Purchase #3	$149.27	12.495%	$167.9213	$167.92	$167.90	$167.90
Purchase #4	$148.51	12.722%	$167.4034	$167.40	$167.40	$167.40
Purchase #5	$165.75	7.141%	$177.5862	$177.59	$177.60	$177.60
Purchase #6	$119.70	3.316%	$123.6693	$123.67	$123.65	$123.70
Purchase #7	$37.85	12.845%	$42.7118	$42.71	$42.70	$42.70
7 purchase totals =	$907.53		$998.9060	$998.91	$998.90	$998.90