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	$189.73	10.493%	$209.6384	$209.64	$209.65	$209.60
Purchase #2	$34.65	12.788%	$39.081	$39.08	$39.10	$39.10
Purchase #3	$63.80	13.638%	$72.501	$72.50	$72.50	$72.50
Purchase #4	$206.95	12.669%	$233.1685	$233.17	$233.15	$233.20
Purchase #5	$38.41	12.827%	$43.3369	$43.34	$43.35	$43.30
Purchase #6	$124.91	7.748%	$134.588	$134.59	$134.60	$134.60
Purchase #7	$116.45	9.389%	$127.3835	$127.38	$127.40	$127.40
7 purchase totals =	$774.90		$859.6973	$859.70	$859.75	$859.70