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	$139.81	13.222%	$158.2957	$158.30	$158.30	$158.30
Purchase #2	$118.78	4.122%	$123.6761	$123.68	$123.70	$123.70
Purchase #3	$163.87	5.573%	$173.0025	$173.00	$173.00	$173.00
Purchase #4	$82.32	10.470%	$90.9389	$90.94	$90.95	$90.90
Purchase #5	$153.56	10.594%	$169.8281	$169.83	$169.85	$169.80
Purchase #6	$63.94	13.628%	$72.6537	$72.65	$72.65	$72.70
Purchase #7	$6.36	7.685%	$6.8488	$6.85	$6.85	$6.80
7 purchase totals =	$728.64		$795.2438	$795.25	$795.30	$795.20