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	$54.61	4.464%	$57.0478	$57.05	$57.05	$57.00
Purchase #2	$54.52	5.414%	$57.4717	$57.47	$57.45	$57.50
Purchase #3	$80.38	6.364%	$85.4954	$85.50	$85.50	$85.50
Purchase #4	$73.78	13.527%	$83.7602	$83.76	$83.75	$83.80
Purchase #5	$130.88	8.269%	$141.7025	$141.70	$141.70	$141.70
Purchase #6	$30.31	12.508%	$34.1012	$34.10	$34.10	$34.10
Purchase #7	$50.95	10.686%	$56.3945	$56.39	$56.40	$56.40
7 purchase totals =	$475.43		$515.9733	$515.97	$515.95	$516.00