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	$16.91	8.866%	$18.4092	$18.41	$18.40	$18.40
Purchase #2	$66.35	9.537%	$72.6778	$72.68	$72.70	$72.70
Purchase #3	$169.86	9.372%	$185.7793	$185.78	$185.80	$185.80
Purchase #4	$59.92	12.151%	$67.2009	$67.20	$67.20	$67.20
Purchase #5	$126.72	8.672%	$137.7092	$137.71	$137.70	$137.70
Purchase #6	$37.80	10.411%	$41.7354	$41.74	$41.75	$41.70
Purchase #7	$95.25	5.728%	$100.7059	$100.71	$100.70	$100.70
7 purchase totals =	$572.81		$624.2177	$624.23	$624.25	$624.20