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	$20.62	9.174%	$22.5117	$22.51	$22.50	$22.50
Purchase #2	$142.46	6.430%	$151.6202	$151.62	$151.60	$151.60
Purchase #3	$104.85	10.508%	$115.8676	$115.87	$115.85	$115.90
Purchase #4	$20.85	9.406%	$22.8112	$22.81	$22.80	$22.80
Purchase #5	$155.74	5.651%	$164.5409	$164.54	$164.55	$164.50
Purchase #6	$40.37	8.128%	$43.6513	$43.65	$43.65	$43.70
Purchase #7	$63.82	6.326%	$67.8573	$67.86	$67.85	$67.90
7 purchase totals =	$548.71		$588.8602	$588.86	$588.80	$588.90