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	$21.64	13.408%	$24.5415	$24.54	$24.55	$24.50
Purchase #2	$77.34	6.105%	$82.0616	$82.06	$82.05	$82.10
Purchase #3	$77.56	10.320%	$85.5642	$85.56	$85.55	$85.60
Purchase #4	$246.31	7.778%	$265.468	$265.47	$265.45	$265.50
Purchase #5	$129.37	5.594%	$136.607	$136.61	$136.60	$136.60
Purchase #6	$119.65	4.694%	$125.2664	$125.27	$125.25	$125.30
Purchase #7	$123.80	8.854%	$134.7613	$134.76	$134.75	$134.80
7 purchase totals =	$795.67		$854.2700	$854.27	$854.20	$854.40