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	$136.90	6.358%	$145.6041	$145.60	$145.60	$145.60
Purchase #2	$152.89	13.667%	$173.7855	$173.79	$173.80	$173.80
Purchase #3	$91.77	13.140%	$103.8286	$103.83	$103.85	$103.80
Purchase #4	$105.86	7.378%	$113.6704	$113.67	$113.65	$113.70
Purchase #5	$37.82	9.376%	$41.366	$41.37	$41.35	$41.40
Purchase #6	$107.51	6.736%	$114.7519	$114.75	$114.75	$114.80
Purchase #7	$91.84	13.208%	$103.9702	$103.97	$103.95	$104.00
7 purchase totals =	$724.59		$796.9767	$796.98	$796.95	$797.10