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	$48.88	12.567%	$55.0227	$55.02	$55.00	$55.00
Purchase #2	$178.39	8.612%	$193.7529	$193.75	$193.75	$193.80
Purchase #3	$89.61	10.552%	$99.0656	$99.07	$99.05	$99.10
Purchase #4	$99.78	3.353%	$103.1256	$103.13	$103.15	$103.10
Purchase #5	$184.81	8.425%	$200.3802	$200.38	$200.40	$200.40
Purchase #6	$54.52	11.748%	$60.925	$60.93	$60.95	$60.90
Purchase #7	$127.90	4.460%	$133.6043	$133.60	$133.60	$133.60
7 purchase totals =	$783.89		$845.8763	$845.88	$845.90	$845.90