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	$25.81	5.396%	$27.2027	$27.20	$27.20	$27.20
Purchase #2	$63.87	4.220%	$66.5653	$66.57	$66.55	$66.60
Purchase #3	$33.49	13.222%	$37.918	$37.92	$37.90	$37.90
Purchase #4	$65.66	9.208%	$71.706	$71.71	$71.70	$71.70
Purchase #5	$127.67	13.138%	$144.4433	$144.44	$144.45	$144.40
Purchase #6	$158.82	12.126%	$178.0785	$178.08	$178.10	$178.10
Purchase #7	$50.84	4.776%	$53.2681	$53.27	$53.25	$53.30
7 purchase totals =	$526.16		$579.1819	$579.19	$579.15	$579.20