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	$151.33	6.267%	$160.8139	$160.81	$160.80	$160.80
Purchase #2	$150.47	11.277%	$167.4385	$167.44	$167.45	$167.40
Purchase #3	$45.84	12.391%	$51.52	$51.52	$51.50	$51.50
Purchase #4	$12.91	13.118%	$14.6035	$14.60	$14.60	$14.60
Purchase #5	$78.34	13.330%	$88.7827	$88.78	$88.80	$88.80
Purchase #6	$34.82	13.237%	$39.4291	$39.43	$39.45	$39.40
Purchase #7	$173.80	5.314%	$183.0357	$183.04	$183.05	$183.00
7 purchase totals =	$647.51		$705.6234	$705.62	$705.65	$705.50