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	$119.72	12.257%	$134.3941	$134.39	$134.40	$134.40
Purchase #2	$49.65	3.816%	$51.5446	$51.54	$51.55	$51.50
Purchase #3	$109.57	13.566%	$124.4343	$124.43	$124.45	$124.40
Purchase #4	$108.86	5.845%	$115.2229	$115.22	$115.20	$115.20
Purchase #5	$39.65	4.108%	$41.2788	$41.28	$41.30	$41.30
Purchase #6	$44.39	8.162%	$48.0131	$48.01	$48.00	$48.00
Purchase #7	$71.72	9.769%	$78.7263	$78.73	$78.75	$78.70
7 purchase totals =	$543.56		$593.6141	$593.60	$593.65	$593.50