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	$42.82	10.157%	$47.1692	$47.17	$47.15	$47.20
Purchase #2	$66.90	13.367%	$75.8425	$75.84	$75.85	$75.80
Purchase #3	$166.64	11.238%	$185.367	$185.37	$185.35	$185.40
Purchase #4	$50.95	8.387%	$55.2232	$55.22	$55.20	$55.20
Purchase #5	$55.57	6.173%	$59.0003	$59.00	$59.00	$59.00
Purchase #6	$72.86	12.163%	$81.722	$81.72	$81.70	$81.70
Purchase #7	$20.92	3.257%	$21.6014	$21.60	$21.60	$21.60
7 purchase totals =	$476.66		$525.9256	$525.92	$525.85	$525.90