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	$48.77	8.731%	$53.0281	$53.03	$53.05	$53.00
Purchase #2	$29.35	10.805%	$32.5213	$32.52	$32.50	$32.50
Purchase #3	$146.52	8.274%	$158.6431	$158.64	$158.65	$158.60
Purchase #4	$52.60	3.490%	$54.4357	$54.44	$54.45	$54.40
Purchase #5	$47.87	6.551%	$51.006	$51.01	$51.00	$51.00
Purchase #6	$209.45	10.548%	$231.5428	$231.54	$231.55	$231.50
Purchase #7	$192.63	12.619%	$216.938	$216.94	$216.95	$216.90
7 purchase totals =	$727.19		$798.1150	$798.12	$798.15	$797.90