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	$18.96	12.650%	$21.3584	$21.36	$21.35	$21.40
Purchase #2	$158.41	9.318%	$173.1706	$173.17	$173.15	$173.20
Purchase #3	$43.82	10.410%	$48.3817	$48.38	$48.40	$48.40
Purchase #4	$208.40	12.197%	$233.8185	$233.82	$233.80	$233.80
Purchase #5	$49.86	6.414%	$53.058	$53.06	$53.05	$53.10
Purchase #6	$104.66	10.840%	$116.0051	$116.01	$116.00	$116.00
Purchase #7	$206.51	4.138%	$215.0554	$215.06	$215.05	$215.10
7 purchase totals =	$790.62		$860.8477	$860.86	$860.80	$861.00