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	$77.59	13.428%	$88.0088	$88.01	$88.00	$88.00
Purchase #2	$98.91	5.346%	$104.1977	$104.20	$104.20	$104.20
Purchase #3	$15.50	7.142%	$16.607	$16.61	$16.60	$16.60
Purchase #4	$176.47	7.859%	$190.3388	$190.34	$190.35	$190.30
Purchase #5	$57.62	13.687%	$65.5064	$65.51	$65.50	$65.50
Purchase #6	$61.86	10.128%	$68.1252	$68.13	$68.15	$68.10
Purchase #7	$136.66	10.437%	$150.9232	$150.92	$150.90	$150.90
7 purchase totals =	$624.61		$683.7071	$683.72	$683.70	$683.60