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	$150.30	5.528%	$158.6086	$158.61	$158.60	$158.60
Purchase #2	$155.67	11.161%	$173.0443	$173.04	$173.05	$173.00
Purchase #3	$54.78	7.856%	$59.0835	$59.08	$59.10	$59.10
Purchase #4	$82.69	13.351%	$93.7299	$93.73	$93.75	$93.70
Purchase #5	$32.72	5.317%	$34.4597	$34.46	$34.45	$34.50
Purchase #6	$110.74	7.172%	$118.6823	$118.68	$118.70	$118.70
Purchase #7	$19.69	4.848%	$20.6446	$20.64	$20.65	$20.60
7 purchase totals =	$606.59		$658.2529	$658.24	$658.30	$658.20