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	$19.35	11.508%	$21.5768	$21.58	$21.60	$21.60
Purchase #2	$232.38	13.647%	$264.0929	$264.09	$264.10	$264.10
Purchase #3	$105.37	9.209%	$115.0735	$115.07	$115.05	$115.10
Purchase #4	$107.30	11.345%	$119.4732	$119.47	$119.45	$119.50
Purchase #5	$110.47	3.837%	$114.7087	$114.71	$114.70	$114.70
Purchase #6	$150.70	12.253%	$169.1653	$169.17	$169.15	$169.20
Purchase #7	$200.32	6.243%	$212.826	$212.83	$212.85	$212.80
7 purchase totals =	$925.89		$1,016.9164	$1,016.92	$1,016.90	$1,017.00