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	$21.70	13.694%	$24.6716	$24.67	$24.65	$24.70
Purchase #2	$174.91	5.839%	$185.123	$185.12	$185.10	$185.10
Purchase #3	$194.79	3.670%	$201.9388	$201.94	$201.95	$201.90
Purchase #4	$73.85	6.369%	$78.5535	$78.55	$78.55	$78.60
Purchase #5	$76.45	8.688%	$83.092	$83.09	$83.10	$83.10
Purchase #6	$146.75	4.523%	$153.3875	$153.39	$153.40	$153.40
Purchase #7	$122.78	13.657%	$139.5481	$139.55	$139.55	$139.50
7 purchase totals =	$811.23		$866.3145	$866.31	$866.30	$866.30