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	$127.72	12.564%	$143.7667	$143.77	$143.75	$143.80
Purchase #2	$49.86	9.216%	$54.4551	$54.46	$54.45	$54.50
Purchase #3	$203.77	10.647%	$225.4654	$225.47	$225.45	$225.50
Purchase #4	$125.35	7.245%	$134.4316	$134.43	$134.45	$134.40
Purchase #5	$158.29	12.856%	$178.6398	$178.64	$178.65	$178.60
Purchase #6	$99.72	9.374%	$109.0678	$109.07	$109.05	$109.10
Purchase #7	$19.92	6.543%	$21.2234	$21.22	$21.20	$21.20
7 purchase totals =	$784.63		$867.0498	$867.06	$867.00	$867.10